#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define isz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
void remin(auto &x, const auto &y) { if (x > y) x = y; }
void remax(auto &x, const auto &y) { if (x < y) x = y; }
using ll = long long;
using ld = long double;
using pii = std::pair<int,int>;
using vi = std::vector<int>;
using vpii = std::vector<pii>;
using vvpii = std::vector<vpii>;
using tiii = std::tuple<int,int,int>;
using vtiii = std::vector<tiii>;
#ifndef __GEOMA_HPP__
#define __GEOMA_HPP__
namespace algos {
namespace geoma {

template<typename A, typename B>
inline std::pair<A,B> operator-(const std::pair<A,B> &a, const std::pair<A,B> &b) {
    return std::pair<A,B>(a.first - b.first, a.second - b.second);
}
template<typename A, typename B>
inline std::pair<A,B> operator+(const std::pair<A,B> &a, const std::pair<A,B> &b) {
    return std::pair<A,B>(a.first + b.first, a.second + b.second);
}

template<typename T, typename A, typename B>
inline T cross(const std::pair<A,B> &a, const std::pair<A,B> &b) {
    return T(a.first) * b.second - T(a.second) * b.first;
}

template<typename T, typename A, typename B>
inline T doubleSquare(const std::pair<A,B> &a, const std::pair<A,B> &b, const std::pair<A,B> &c) {
    T res = cross<T>(a-b, c-b);
    if (res < 0)
        res = -res;
    return res;
}

template<typename T, typename A, typename B>
inline T dist2(const std::pair<A,B> &a) {
    return T(a.first)*a.first + T(a.second)*a.second;
}

template<typename T, typename A, typename B>
inline T dist2(const std::pair<A, B> &a, const std::pair<A, B> &b) {
    return dist2<T>(a-b);
}

using Triangle = std::tuple<pii,pii,pii>;

inline bool isPointInsideTriangle(Triangle tr, pii p) {
    auto [A, B, C] = tr;
    auto S = doubleSquare<ll>(A,B,C);
    auto S1 = doubleSquare<ll>(p,B,C);
    auto S2 = doubleSquare<ll>(A,p,C);
    auto S3 = doubleSquare<ll>(A,B,p);
    return S == S1 + S2 + S3;
}

inline ll orientedSquare(const std::vector<pii> &points) {
    ll res = cross<ll>(points.back(), points.front());
    for (int i = 0; i + 1 < isz(points); i++)
        res += cross<ll>(points[i], points[i+1]);
    return res;
}

inline vpii readPolygon() {
    int n;
    vpii points;
    std::cin >> n;
    points.resize(n);
    for (auto &[x,y] : points)
        std::cin >> x >> y;
    return points;
}

inline void moveToPositive(vpii &points) {
    int minX = INT_MAX, minY = INT_MAX;
    for (auto &[x,y] : points) {
        remin(minX, x);
        remin(minY, y);
    }
    if (minX % 2 != 0) minX--;
    if (minY % 2 != 0) minY--;
    for (auto &[x,y] : points)
        x -= minX, y -= minY;
}

inline void transpose(vpii &points) {
    for (auto &[x,y] : points)
        std::swap(x, y);
}

inline void makeCounterClockwise(vpii &points) {
    ll sq = orientedSquare(points);
    if (sq < 0) std::reverse(all(points));
}

inline int sign(auto x) { return x < 0 ? -1 : (x > 0 ? +1 : 0); }

const int LEFT = -1, RIGHT = +1;

inline int rotation(pii first, pii mid, pii last) {
// > 0 --> right
// < 0 --> left
    return sign(cross<ll>(first-mid,last-mid));
}

inline bool isPointOnSegment(pii P, pii A, pii B) {
    auto [x, y] = P;
    auto [xmin,xmax] = std::minmax({A.first, B.first});
    auto [ymin,ymax] = std::minmax({A.second, B.second});
    if (x < xmin || x > xmax || y < ymin || y > ymax)
        return false;
    return cross<ll>(A-P,B-P) == 0;
}

const int NONE = 0, POINT = 1, INSIDE = 2;
inline int intersects(pii A, pii B, pii C, pii D) {
    if (A == C || A == D || B == C || B == D)
        return POINT;
    if (isPointOnSegment(A,C,D) || isPointOnSegment(B,C,D) ||
        isPointOnSegment(C,A,B) || isPointOnSegment(D,A,B))
        return POINT;
    auto [xmin1,xmax1] = std::minmax({A.first, B.first});
    auto [ymin1,ymax1] = std::minmax({A.second, B.second});
    auto [xmin2,xmax2] = std::minmax({C.first, D.first});
    auto [ymin2,ymax2] = std::minmax({C.second, D.second});
    if (xmax1 < xmin2 || xmin1 > xmax2)
        return NONE;
    if (ymax1 < ymin2 || ymin1 > ymax2)
        return NONE;
    auto rot1 = rotation(A,B,C);
    auto rot2 = rotation(A,B,D);
    if (sign(rot1) * sign(rot2) < 0)
        return INSIDE;
    return NONE;
}

inline bool isAlmostEqual(ld x, ld y) {
    const ld EPS = 1e-10;
    return std::abs(x-y) / (1 + std::abs(x)) < EPS;
}

inline bool angleLessThanPi(pii L, pii M, pii R) {
    return rotation(L,M,R) == LEFT;
}

inline bool angleGreaterThanPi(pii L, pii M, pii R) {
    return rotation(L,M,R) == RIGHT;
}

inline auto getPrev(const auto &vec, int i) {
    i--;
    if (i < 0) i = isz(vec)-1;
    return vec[i];
}

inline auto getNext(const auto &vec, int i) {
    i++;
    if (i == isz(vec))
        i = 0;
    return vec[i];
}

inline bool isConvex(const vpii &P) {
    for (int i = 0; i < isz(P); i++)
        if (rotation(getPrev(P, i), P[i], getNext(P, i)) == RIGHT)
            return false;
    return true;
}

inline void removeSameLine(vpii &P) {
    static std::vector<bool> keep;
    keep.assign(isz(P), false);
    for (int i = 0; i < isz(P); i++)
        keep[i] = (rotation(getPrev(P,i), P[i], getNext(P,i)) != 0);
    int p = 0;
    for (int i = 0; i < isz(P); i++)
        if (keep[i]) P[p++] = P[i];
    P.resize(p);
}

} // namespace geoma
} // namespace algos
#endif // __GEOMA_HPP__
#ifndef __TRIANGULATE_HPP__
#define __TRIANGULATE_HPP__
namespace algos {
namespace triangulate {

using namespace geoma;

inline bool liesBelow(pii P1, pii P2) {
    auto [x1,y1] = P1;
    auto [x2,y2] = P2;
    return (y1 < y2 || (y1 == y2 && x1 > x2));
}

inline bool liesAbove(pii P1, pii P2) {
    auto [x1,y1] = P1;
    auto [x2,y2] = P2;
    return (y1 > y2 || (y1 == y2 && x1 < x2));
}

const int START = 0, SPLIT = 1, END = 2, MERGE = 3, REGULAR = 4;

inline auto getTypeOfVertex(const auto &P, int i) {
    pii L = getPrev(P, i), M = P[i], R = getNext(P, i);
    if (liesBelow(L,M) && liesBelow(R,M) && angleLessThanPi(L,M,R))
        return START;
    if (liesBelow(L,M) && liesBelow(R,M) && angleGreaterThanPi(L,M,R))
        return SPLIT;
    if (liesAbove(L,M) && liesAbove(R,M) && angleLessThanPi(L,M,R))
        return END;
    if (liesAbove(L,M) && liesAbove(R,M) && angleGreaterThanPi(L,M,R))
        return MERGE;
    return REGULAR;
}

inline std::string type2str(int t) {
    switch(t) {
        case START: return "start";
        case SPLIT: return "split";
        case END: return "end";
        case MERGE: return "merge";
        case REGULAR: return "regular";
        default: return "none";
    };
}

inline bool isMonotone(const vpii &P) {
    if (isz(P) <= 3)
        return true;
    // we should start from max vertex
    int imax = -1, ymax = INT_MIN;
    for (int i = 0; i < isz(P); i++)
        if (P[i].second >= ymax) {
            imax = i;
            ymax = P[i].second;
        }
    int len = 0;
    int i = imax;
    while (len <= isz(P) && P[i].second >= getNext(P, i).second) {
        len++;
        i++;
        if (i == isz(P)) i = 0;
    }
    while (len <= isz(P) && P[i].second <= getNext(P, i).second) {
        len++;
        i++;
        if (i == isz(P)) i = 0;
    }
    return len >= isz(P);
}

inline vpii findDiagonals(const vpii &P) {
    static vtiii pq;
    pq.clear();
    for (int i = 0; i < isz(P); i++) {
        auto [x,y] = P[i];
        pq.emplace_back(y,-x,i);
    }
    std::sort(all(pq), std::greater<>());
    int currY, currX;
    auto setCurrY = [&](int newCurrY) { currY = newCurrY; };
    auto setCurrX = [&](int newCurrX) { currX = newCurrX; };

    static vi helper;
    helper.assign(isz(P),-1);
    
    auto getHelper = [&](int i) {
        if (i < 0) i += isz(P);
        assert(0 <= i && i < isz(P));
        assert(helper[i] != -1);
        return helper[i];
    };
    auto setHelper = [&](int i, int j) {
        if (i < 0) i += isz(P);
        assert(0 <= i && i < isz(P));
        if (helper[i] == i)
            helper[i] = j;
        else if (helper[i] != -1) {
            if (int k = helper[i]; P[k].second > P[j].second)
                helper[i] = j;
        } else
            helper[i] = j;
    };
    auto getEdge = [&](int i) {
        if (i < 0) i += isz(P);
        if (i >= isz(P)) i -= isz(P);
        auto L = P[i], R = getNext(P, i);
        auto [ymin, ymax] = std::minmax({L.second, R.second});
        return tiii(ymin, ymax, i);
    };
    auto getEdgeId = [&](int i) {
        auto [y1,y2,j] = getEdge(i);
        if (y1 == y2) return -1;
        return j;
    };
    
    int cachedId = -1;
    ld cachedX = -1;
    auto isCached = [&](int id) { return id == cachedId; };
    auto setCached = [&](int id, ld x) { cachedId = id; cachedX = x; };
    auto clearCached = [&](){cachedId = -1; cachedX = -1;};
    
    auto coordOfIntersection = [&](int i, int y) -> ld {
        if (i < 0) i += isz(P);
        if (isCached(i))
            return cachedX;
        assert(0 <= i && i < isz(P));
        auto [x1,y1] = P[i];
        auto [x2,y2] = getNext(P, i);
        //ld B = ld(x2-x1)/(y2-y1);
        //ld A = x1 - y1 * B;
        // x1 - y1 * (x2-x1)/(y2-y1)
        // x1 - y1 * (x2-x1)/(y2-y1) + y * (x2-x1)/(y2-y1)
        // (x1 * (y2 - y1) + (y - y1) * (x2 - x1)) / (y2 - y1)
        // (x1 * y2 + y * x2 - y * x1 - y1 * x2) / (y2 - y1)
        assert(y2 != y1);
        return ld((ld)x1 * y2 + (ld)y * x2 - (ld)y * x1 - (ld)y1 * x2) / (y2 - y1);
    };
    auto LessByIntersection = [&](const int &j1, const int &j2) {
        ld x1 = coordOfIntersection(j1, currY);
        ld x2 = coordOfIntersection(j2, currY);
        if (x1 > x2) return false;
        if (x1 < x2) return true;
        return j1 < j2;
    };
    // y1 + t * (y2-y1) = y => t = (y - y1)/(y2 - y1)
    // x1 + t * (x2-x1) = x => x1 + (y - y1) * (x2-x1) / (y2 - y1)
    // coeff = (x2 - x1) / (y2 - y1)
    // x1 + (y - y1) * coeff <= x
    // x1 - y1 * coeff + y * coeff <= x
    // A + y * B <= x -- need to sort by these values
    std::set<int, decltype(LessByIntersection)> T(LessByIntersection);
    
    auto insertEdgeInT = [&](int i) {
        int ei = getEdgeId(i);
        if (ei == -1) return;
        auto y = P[i].second;
        setCurrY(y);
        setCached(ei, coordOfIntersection(ei, currY));
        T.insert(ei);
        clearCached();
    };
    auto deleteEdgeFromT = [&](int i) {
        int j = getEdgeId(i);
        if (j == -1) return;
        auto it = T.find(j);
        assert(it != T.end());
        T.erase(it);
    };
    
    auto searchEdgeInT = [&](int i) {
        assert(0 <= i && i < isz(P));
        const auto [x, y] = P[i];
        setCurrY(y); setCurrX(x);
        int cand;
        setCached(isz(P), x);
        auto it = T.upper_bound(isz(P));
        assert(it != T.begin());
        cand = *std::prev(it);
        clearCached();
        return cand;
    };
    vpii diagonals;
    auto addEdgeInTriangles = [&](int u, int v) {
        if (getNext(P, u) != P[v] && getPrev(P, u) != P[v])
            diagonals.emplace_back(u,v);
    };
    for (auto [y,x,i] : pq) {
        x *= -1;
        setCurrY(y);
        switch (getTypeOfVertex(P,i)) {
            case START: {
                insertEdgeInT(i);
                setHelper(i, i);
                break;
            }
            case END: {
                addEdgeInTriangles(i, getHelper(i-1));
                deleteEdgeFromT(i-1);
                break;
            }
            case SPLIT: {
                int j = searchEdgeInT(i);
                addEdgeInTriangles(i, getHelper(j));
                setHelper(j, i);
                insertEdgeInT(i);
                setHelper(i, i);
                break;
            }
            case MERGE: {
                addEdgeInTriangles(i, getHelper(i-1));
                deleteEdgeFromT(i-1);
                int j = searchEdgeInT(i);
                addEdgeInTriangles(i, getHelper(j));
                setHelper(j, i);
                break;
            }
            case REGULAR: {
                if (liesAbove(getPrev(P,i), P[i]) && liesBelow(getNext(P,i), P[i])) {
                    addEdgeInTriangles(i, getHelper(i-1));
                    deleteEdgeFromT(i-1);
                    insertEdgeInT(i);
                    setHelper(i, i);
                } else {
                    int j = searchEdgeInT(i);
                    addEdgeInTriangles(i, getHelper(j));
                    setHelper(j, i);
                }
                break;
            }
        };
    }
    return diagonals;
}

struct Node {
    const vpii * parent = nullptr;
    Node * next = nullptr;
    Node * prev = nullptr;
    int where{}, id{};
    std::list<int> diagonals{};
    
    void setNext(Node *n) {
        next = n;
        n->prev = this;
    }
    void setPrev(Node *n) {
        prev = n;
        n->next = this;
    }
    vpii to_vector() const {
        vpii result(1, (*parent)[id]);
        for (Node *it = next; it != this; it = it->next)
            result.push_back((*parent)[it->id]);
        return result;
    }
    pii to_point() const {
        return (*parent)[id];
    }
};

template<typename Func>
inline void splitByDiag(const vpii &P, const vpii &D, const Func &f) {
    if (isz(P) <= 2)
        return;
    if (isz(P) == 3) {
        assert(D.empty());
        f(P);
        return;
    }
    static std::vector<Node *> nodes;
    nodes.clear();
    for (int i = 0; i < isz(P); i++)
        nodes.emplace_back(new Node{&P, nullptr, nullptr, 0, i, {}});
    for (int i = 0; i+1 < isz(nodes); i++)
        nodes[i]->setNext(nodes[i+1]);
    nodes.front()->setPrev(nodes.back());
    static std::vector<std::pair<Node*, Node*>> diagonals;
    diagonals.clear();
    for (const auto &[u,v] : D) {
        assert(0 <= u && u < isz(nodes));
        assert(0 <= v && v < isz(nodes));
        int currDiag = isz(diagonals);
        diagonals.push_back({nodes[u], nodes[v]});
        nodes[u]->diagonals.push_back(currDiag);
        nodes[v]->diagonals.push_back(currDiag);
    }

    int cntPoly = 1;
    for (int id = 0; id < isz(diagonals); id++) {
        // need to split by this diagonal
        auto [startFi, startSe] = diagonals[id];
        auto currFi = startFi, currSe = startSe;
        while (currFi != startSe && currSe != startFi) {
            currFi = currFi->next;
            currSe = currSe->next;
        }
        // need to copy ends of diagonal:
        nodes.push_back(new Node{&P, nullptr, nullptr, cntPoly, startFi->id, {}});
        Node *copyFi = nodes.back();
        nodes.push_back(new Node{&P, nullptr, nullptr, cntPoly, startSe->id, {}});
        Node *copySe = nodes.back();
        // choose a list with min len:
        if (currFi != startSe) {
            std::swap(copyFi, copySe);
            std::swap(startFi, startSe);
            std::swap(currFi, currSe);
        }
        assert(currFi == startSe);
        // iterate over all vertices and updates diagonals
        for (currFi = currFi->prev; currFi != startFi; currFi = currFi->prev) {
            auto &dd = currFi->diagonals;
            for (auto it = dd.begin(); it != dd.end(); ) {
                // this diagonal still exists?
                if (*it <= id) {
                    it = dd.erase(it);
                    continue;
                }
                auto &[lhs, rhs] = diagonals[*it];
                if (lhs == startFi) (lhs = copyFi)->diagonals.push_back(*it);
                if (rhs == startFi) (rhs = copyFi)->diagonals.push_back(*it);
                if (lhs == startSe) (lhs = copySe)->diagonals.push_back(*it);
                if (rhs == startSe) (rhs = copySe)->diagonals.push_back(*it);
                it = std::next(it);
            }
            // set where this vertex lies
            currFi->where = cntPoly;
        }
        // disconnect less half:
        copyFi->setNext(currFi->next);
        copySe->next = copyFi;
        copySe->setNext(copyFi);
        startSe->prev->setNext(copySe);
        startFi->setNext(startSe);
        cntPoly++;
    }
    static std::vector<Node *> anyNode;
    anyNode.resize(cntPoly);
    for (auto it : nodes)
        anyNode[it->where] = it;
    for (int i = 0; i < cntPoly; i++) {
        vpii temp = anyNode[i]->to_vector();
        removeSameLine(temp);
        //assert(isMonotone(temp));
        f(temp);
    }
    for (auto node : nodes)
        delete node;
}

inline vvpii splitByDiag(const vpii &P, const vpii &D) {
    vvpii result;
    splitByDiag(P, D, [&](const vpii &PP){ result.push_back(PP); });
    return result;
}

inline vpii TriangulateMonotonePolygon(const vpii &P) {
    if (isz(P) <= 3)
        return {};
    // we need to create chains
    int ymax = INT_MIN, ymin = INT_MAX, imax = -1;
    int leftChainBegin = -1, leftChainEnd = -1;
    for (int i = 0; i < isz(P); i++) {
        if (P[i].second >= ymax) {
            imax = i;
            ymax = P[i].second;
        }
        if (P[i].second == ymax && getNext(P, i).second != ymax) {
            leftChainBegin = i;
        }
        remin(ymin, P[i].second);
    }
    
    const int LEFT_CHAIN = 0,  RIGHT_CHAIN = 1;
    assert(imax != -1);
    static vi chainType; chainType.assign(isz(P), -1);
    static vi chainPos; chainPos.assign(isz(P), -1);
    assert(leftChainBegin != -1);
    leftChainEnd = leftChainBegin;
    int pos = 0;
    while (!(P[leftChainEnd].second == ymin && getPrev(P, leftChainEnd).second != ymin)) {
        chainType[leftChainEnd] = LEFT_CHAIN;
        chainPos[leftChainEnd] = pos++;
        leftChainEnd++;
        if (leftChainEnd == isz(P))
            leftChainEnd = 0;
    }
    chainType[leftChainEnd] = LEFT_CHAIN;
    if (chainPos[leftChainEnd] == -1)
        chainPos[leftChainEnd] = pos++;
    pos = 0;
    for (int i = (leftChainBegin-1+isz(P)) % isz(P); chainType[i] == -1; ) {
        chainType[i] = RIGHT_CHAIN;
        chainPos[i] = pos++;
        i--;
        if (i < 0) i = isz(P)-1;
    }
    // {y-coord, chainId, posInChain}
    auto cmp = [&](pii a, pii b) {
        auto [ya, ida] = a;
        auto [yb, idb] = b;
        if (ya < yb) return true;
        if (ya > yb) return false;
        if (chainType[ida] != chainType[idb]) {
            return chainType[ida] < chainType[idb];
        }
        return chainPos[ida] > chainPos[idb];
    };
    static vpii pq;
    pq.clear();
    for (int i = 0; i < isz(P); i++) {
        auto [x,y] = P[i];
        pq.push_back({y,i});
    }
    std::sort(pq.rbegin(), pq.rend(), cmp);
    static vi S;
    S.clear();
    S.push_back(std::get<1>(pq[0]));
    S.push_back(std::get<1>(pq[1]));
    
    vpii diagonals;
    auto addDiagonal = [&](int i, int j) {
        if (getNext(P, i) != P[j] && getPrev(P, i) != P[j]) {
            diagonals.emplace_back(i, j);
            return true;
        }
        return false;
    };
    auto isSameChain = [&](int i, int j) {
        return chainType[i] == chainType[j];
    };
    
    for (const auto &[y, id] : pq) {
        if (!isSameChain(id,S.back())) {
            int last = S.back();
            while (isz(S) > 1) {
                addDiagonal(id, S.back());
                S.pop_back();
            }
            S = {last, id};
        } else {
            int want = LEFT, skip = RIGHT;
            if (chainType[id] == LEFT_CHAIN)
                std::swap(want, skip);
            pii first = P[id];
            while (isz(S) >= 2) {
                pii mid = P[S[isz(S)-1]];
                pii last = P[S[isz(S)-2]];
                ll rot = rotation(first, mid, last);
                if (rot == skip)
                    break;
                if (rot != want) {
                    S.pop_back();
                    continue;
                }
                assert(rot == want);
                addDiagonal(id, S[isz(S)-2]);
                S.pop_back();
            }
            S.push_back(id);
        }
    }
    return diagonals;
}

template<typename Func>
inline void triangulateFast(vpii inP, const Func &f) {
    ll fullSquare = orientedSquare(inP);
    removeSameLine(inP);
    vpii D = findDiagonals(inP);
    splitByDiag(inP, D, [&](vpii PP){
        removeSameLine(PP);
        vpii DD = TriangulateMonotonePolygon(PP);
        auto ff = [&](const vpii &t){
            fullSquare -= orientedSquare(t);
            f(t);
        };
        splitByDiag(PP, DD, ff);
    });
    assert(fullSquare == 0);
}

inline std::vector<Triangle> triangulateFast(const vpii &inP) {
    std::vector<Triangle> answ;
    triangulateFast(inP, [&](const vpii &t){
        assert(isz(t) <= 3);
        if (isz(t) == 3) answ.emplace_back(t[0], t[1], t[2]);
    });
    return answ;
}

inline std::vector<Triangle> triangulateSlow(const vpii &points)
{
// slow triangulation in time O(n^2)
    std::vector<Triangle> triangles;
    std::list<pii> list(all(points));
    while (isz(list) > 3) {
        // search a vertex which we can cut off:
        for (auto it = list.begin(); it != list.end(); ) {
            auto next = (std::next(it) == list.end() ? list.begin() : std::next(it));
            auto prev = (it == list.begin() ? std::prev(list.end()) : std::prev(it));
            ll rot = rotation(*prev, *it, *next);
            if (rot == 0) {
                it = list.erase(it);
            } else if (rot < 0) {
                // check this vertex:
                bool ok = true;
                for (auto p : list) {
                    bool bad = isPointInsideTriangle({*prev, *it, *next}, p);
                    bad = bad && !isPointOnSegment(p, *prev, *it);
                    bad = bad && !isPointOnSegment(p, *it, *next);
                    bad = bad && !isPointOnSegment(p, *prev, *next);
                    if (bad) {
                        ok = false;
                        break;
                    }
                }
                if (ok) {
                    triangles.emplace_back(*prev, *it, *next);
                    it = list.erase(it);
                } else {
                    it++;
                }
            } else {
                it++;
            }
        }
    }
    if (isz(list) == 3)
        triangles.emplace_back(*list.begin(), *(++list.begin()), *(++++list.begin()));
    else assert(isz(list) < 3);
    return triangles;
}

inline std::vector<Triangle> triangulateConvex(const vpii &points) {
// points is convex polygon
// take any vertex and make triangles
    std::vector<Triangle> triangles;
    for (int i = 1; i + 1 < isz(points); i++)
        triangles.emplace_back(points[0], points[i], points[i+1]);
    return triangles;
}

inline std::vector<Triangle> triangulate(vpii points) {
    makeCounterClockwise(points);
    return triangulateFast(points);
}

} // namespace triangulate
} // namespace algos
#endif // __TRIANGULATE_HPP__
using namespace algos::triangulate;
using namespace algos::geoma;

pii pickPointOutside(pii A, pii B) {
    pii C1(A.first, B.second);
    pii C2(B.first, A.second);
    pii res = cross<ll>(A-C1, B-C1) < 0 ? C1 : C2;
    return res;
}

std::pair<ld,ld> rectangle(int xmin, int ymin, int xmax, int ymax) {
    ll dx = xmax - xmin, dy = ymax - ymin;
    ld fi = (dx + 1) / 2 * dy;
    ld se = dx / 2 * dy;
    if (xmin % 2 != 0) std::swap(fi,se);
    return {fi, se};
}

ll sum(ll n) {
// n^2 - (n-1)^2 + (n-2)^2 - (n-3)^2 + (n-4)^2 + ...
    return n * (n+1) / 2;
}

std::pair<ld, ld> solveBaseCaseLD(ll x, ll y) {
// triangle
// *
// **
// ***
// ****
    ld c = y / (2.0L * x);
    std::pair<ld, ld> res{c * sum(x), c * sum(x-1)};
    return res;
}

std::pair<ld, ld> solveBaseCaseRU(ll x, ll y) {
// triangle
// ****
//  ***
//   **
//    *
    auto res = solveBaseCaseLD(x, y);
    if (x % 2 == 0)
        std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseRU(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
// ****
//  ***
//   **
//    *
    auto res = solveBaseCaseRU(xmax-xmin, ymax-ymin);
    if (xmin % 2 != 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseLD(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
// *
// **
// ***
// ****
    auto res = solveBaseCaseLD(xmax-xmin, ymax-ymin);
    if (xmin % 2 != 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseRD(ll x, ll y) {
// triangle
//    *
//   **
//  ***
// ****
    auto res = solveBaseCaseLD(x, y);
    if (x % 2 == 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseLU(ll x, ll y) {
// triangle
// ****
// ***
// **
// *   
    auto res = solveBaseCaseLD(x, y);
    return res;
}

std::pair<ld, ld> solveBaseCaseLU(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
// ****
// ***
// **
// *
    auto res = solveBaseCaseLU(xmax-xmin, ymax-ymin);
    if (xmin % 2 != 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseRD(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
//    *
//   **
//  ***
// ****
    auto res = solveBaseCaseRD(xmax-xmin,ymax-ymin);
    if (xmin % 2 != 0)
        std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> triangle(pii A, pii B, pii C) {
// B - corner
// AC - diagonal
    if (doubleSquare<ll>(A,B,C) == 0)
        return {0, 0};
    if (A.first > C.first)
        std::swap(A, C);
    ll xmin = std::min({A.first, B.first, C.first});
    ll xmax = std::max({A.first, B.first, C.first});
    ll ymin = std::min({A.second, B.second, C.second});
    ll ymax = std::max({A.second, B.second, C.second});
    pii LD(xmin,ymin), LU(xmin,ymax), RD(xmax,ymin), RU(xmax,ymax);
    std::pair<ld,ld> res;
    if (A.second > C.second) {
        if (B == LD) res = solveBaseCaseLD(xmin,ymin,xmax,ymax);
        else res = solveBaseCaseRU(xmin,ymin,xmax,ymax);
    } else {
        if (B == RD) res = solveBaseCaseRD(xmin,ymin,xmax,ymax);
        else res = solveBaseCaseLU(xmin,ymin,xmax,ymax);
    }
    return res;
}

std::pair<ld,ld> twoRectangles(pii A, pii B, pii C) {
    if (A.first > B.first) std::swap(A, B);
    if (A.first > C.first) std::swap(A, C);
    if (B.first > C.first) std::swap(B, C);
    assert(A.first <= B.first && B.first <= C.first);
    auto [ymin, ymax] = std::minmax({A.second,C.second});
    if (B.second >= ymax || B.second <= ymin || B.first == A.first || B.first == C.first) {
        remin(ymin, B.second);
        remax(ymax, B.second);
        return rectangle(A.first, ymin, C.first, ymax);
    }
    std::pair<ld,ld> rect = rectangle(A.first, ymin, C.first, ymax);
    // above or below than diagonal?
    if (rotation(A,C,B) <= 0) { // above
        // is A below than C?
        if (A.second <= C.second)
            rect = rect - rectangle(A.first, B.second, B.first, ymax);
        else
            rect = rect - rectangle(B.first, B.second, C.first, ymax);
    } else { // below
        // is A below than C?
        if (A.second <= C.second)
            rect = rect - rectangle(B.first, ymin, C.first, B.second);
        else
            rect = rect - rectangle(A.first, ymin, B.first, B.second);
    }
    return rect;
}

std::pair<ld,ld> calcTriangle(pii A, pii B, pii C) {
    if (cross<ll>(A-B,C-B) > 0)
        std::swap(A, C);
    auto temp = twoRectangles(A,B,C);
    auto P1 = pickPointOutside(A,B);
    auto P2 = pickPointOutside(B,C);
    auto P3 = pickPointOutside(C,A);
    if (!(A.first == B.first || A.second == B.second))
        temp = temp - triangle(A,P1,B);
    if (!(B.first == C.first || B.second == C.second))
        temp = temp - triangle(B,P2,C);
    if (!(C.first == A.first || C.second == A.second))
        temp = temp - triangle(C,P3,A);
    return temp;
}

ld solveFast(vpii points) {
    moveToPositive(points);
    transpose(points);
    makeCounterClockwise(points);
    ld answ = 0;
    triangulateFast(points, [&](const vpii &tr){
        assert(isz(tr) <= 3);
        if (isz(tr) == 3)
            answ += calcTriangle(tr[0],tr[1],tr[2]).first;
    });
    return answ;
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    std::cout << std::fixed << std::setprecision(12);
    auto points = readPolygon();
    std::cout << solveFast(points) << std::endl;
}

#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define isz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
void remin(auto &x, const auto &y) { if (x > y) x = y; }
void remax(auto &x, const auto &y) { if (x < y) x = y; }
using ll = long long;
using ld = long double;
using pii = std::pair<int,int>;
using vi = std::vector<int>;
using vpii = std::vector<pii>;
using vvpii = std::vector<vpii>;
using tiii = std::tuple<int,int,int>;
using vtiii = std::vector<tiii>;
#ifndef __GEOMA_HPP__
#define __GEOMA_HPP__
namespace algos {
namespace geoma {

template<typename A, typename B>
inline std::pair<A,B> operator-(const std::pair<A,B> &a, const std::pair<A,B> &b) {
    return std::pair<A,B>(a.first - b.first, a.second - b.second);
}
template<typename A, typename B>
inline std::pair<A,B> operator+(const std::pair<A,B> &a, const std::pair<A,B> &b) {
    return std::pair<A,B>(a.first + b.first, a.second + b.second);
}

template<typename T, typename A, typename B>
inline T cross(const std::pair<A,B> &a, const std::pair<A,B> &b) {
    return T(a.first) * b.second - T(a.second) * b.first;
}

template<typename T, typename A, typename B>
inline T doubleSquare(const std::pair<A,B> &a, const std::pair<A,B> &b, const std::pair<A,B> &c) {
    T res = cross<T>(a-b, c-b);
    if (res < 0)
        res = -res;
    return res;
}

template<typename T, typename A, typename B>
inline T dist2(const std::pair<A,B> &a) {
    return T(a.first)*a.first + T(a.second)*a.second;
}

template<typename T, typename A, typename B>
inline T dist2(const std::pair<A, B> &a, const std::pair<A, B> &b) {
    return dist2<T>(a-b);
}

inline ll orientedSquare(const std::vector<pii> &points) {
    ll res = cross<ll>(points.back(), points.front());
    for (int i = 0; i + 1 < isz(points); i++)
        res += cross<ll>(points[i], points[i+1]);
    return res;
}

inline vpii readPolygon() {
    int n;
    vpii points;
    std::cin >> n;
    points.resize(n);
    for (auto &[x,y] : points)
        std::cin >> x >> y;
    return points;
}

inline void moveToPositive(vpii &points) {
    int minX = INT_MAX, minY = INT_MAX;
    for (auto &[x,y] : points) {
        remin(minX, x);
        remin(minY, y);
    }
    if (minX % 2 != 0) minX--;
    if (minY % 2 != 0) minY--;
    for (auto &[x,y] : points)
        x -= minX, y -= minY;
}

inline void transpose(vpii &points) {
    for (auto &[x,y] : points)
        std::swap(x, y);
}

inline void makeCounterClockwise(vpii &points) {
    ll sq = orientedSquare(points);
    if (sq < 0) std::reverse(all(points));
}

inline int sign(auto x) { return x < 0 ? -1 : (x > 0 ? +1 : 0); }

const int LEFT = -1, RIGHT = +1;

inline int rotation(pii first, pii mid, pii last) {
// > 0 --> right
// < 0 --> left
    return sign(cross<ll>(first-mid,last-mid));
}
} // geoma
} // algos
#endif // __GEOMA_HPP__
using namespace algos::geoma;

pii pickPointOutside(pii A, pii B) {
    pii C1(A.first, B.second);
    pii C2(B.first, A.second);
    pii res = cross<ll>(A-C1, B-C1) < 0 ? C1 : C2;
    return res;
}

std::pair<ld,ld> rectangle(int xmin, int ymin, int xmax, int ymax) {
    ll dx = xmax - xmin, dy = ymax - ymin;
    ld fi = (dx + 1) / 2 * dy;
    ld se = dx / 2 * dy;
    if (xmin % 2 != 0) std::swap(fi,se);
    return {fi, se};
}

ll sum(ll n) {
// n^2 - (n-1)^2 + (n-2)^2 - (n-3)^2 + (n-4)^2 + ...
    return n * (n+1) / 2;
}

std::pair<ld, ld> solveBaseCaseLD(ll x, ll y) {
// triangle
// *
// **
// ***
// ****
    ld c = y / (2.0L * x);
    std::pair<ld, ld> res{c * sum(x), c * sum(x-1)};
    return res;
}

std::pair<ld, ld> solveBaseCaseRU(ll x, ll y) {
// triangle
// ****
//  ***
//   **
//    *
    auto res = solveBaseCaseLD(x, y);
    if (x % 2 == 0)
        std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseRU(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
// ****
//  ***
//   **
//    *
    auto res = solveBaseCaseRU(xmax-xmin, ymax-ymin);
    if (xmin % 2 != 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseLD(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
// *
// **
// ***
// ****
    auto res = solveBaseCaseLD(xmax-xmin, ymax-ymin);
    if (xmin % 2 != 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseRD(ll x, ll y) {
// triangle
//    *
//   **
//  ***
// ****
    auto res = solveBaseCaseLD(x, y);
    if (x % 2 == 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseLU(ll x, ll y) {
// triangle
// ****
// ***
// **
// *   
    auto res = solveBaseCaseLD(x, y);
    return res;
}

std::pair<ld, ld> solveBaseCaseLU(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
// ****
// ***
// **
// *
    auto res = solveBaseCaseLU(xmax-xmin, ymax-ymin);
    if (xmin % 2 != 0) std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> solveBaseCaseRD(ll xmin, ll ymin, ll xmax, ll ymax) {
// triangle
//    *
//   **
//  ***
// ****
    auto res = solveBaseCaseRD(xmax-xmin,ymax-ymin);
    if (xmin % 2 != 0)
        std::swap(res.first, res.second);
    return res;
}

std::pair<ld, ld> triangle(pii A, pii B, pii C) {
// B - corner
// AC - diagonal
    if (doubleSquare<ll>(A,B,C) == 0)
        return {0, 0};
    if (A.first > C.first)
        std::swap(A, C);
    ll xmin = std::min({A.first, B.first, C.first});
    ll xmax = std::max({A.first, B.first, C.first});
    ll ymin = std::min({A.second, B.second, C.second});
    ll ymax = std::max({A.second, B.second, C.second});
    pii LD(xmin,ymin), LU(xmin,ymax), RD(xmax,ymin), RU(xmax,ymax);
    std::pair<ld,ld> res;
    if (A.second > C.second) {
        if (B == LD) res = solveBaseCaseLD(xmin,ymin,xmax,ymax);
        else res = solveBaseCaseRU(xmin,ymin,xmax,ymax);
    } else {
        if (B == RD) res = solveBaseCaseRD(xmin,ymin,xmax,ymax);
        else res = solveBaseCaseLU(xmin,ymin,xmax,ymax);
    }
    return res;
}

std::pair<ld,ld> twoRectangles(pii A, pii B, pii C) {
    if (A.first > B.first) std::swap(A, B);
    if (A.first > C.first) std::swap(A, C);
    if (B.first > C.first) std::swap(B, C);
    assert(A.first <= B.first && B.first <= C.first);
    auto [ymin, ymax] = std::minmax({A.second,C.second});
    if (B.second >= ymax || B.second <= ymin || B.first == A.first || B.first == C.first) {
        remin(ymin, B.second);
        remax(ymax, B.second);
        return rectangle(A.first, ymin, C.first, ymax);
    }
    std::pair<ld,ld> rect = rectangle(A.first, ymin, C.first, ymax);
    // above or below than diagonal?
    if (rotation(A,C,B) <= 0) { // above
        // is A below than C?
        if (A.second <= C.second)
            rect = rect - rectangle(A.first, B.second, B.first, ymax);
        else
            rect = rect - rectangle(B.first, B.second, C.first, ymax);
    } else { // below
        // is A below than C?
        if (A.second <= C.second)
            rect = rect - rectangle(B.first, ymin, C.first, B.second);
        else
            rect = rect - rectangle(A.first, ymin, B.first, B.second);
    }
    return rect;
}

std::pair<ld,ld> calcTriangle(pii A, pii B, pii C) {
    if (cross<ll>(A-B,C-B) > 0)
        std::swap(A, C);
    auto temp = twoRectangles(A,B,C);
    auto P1 = pickPointOutside(A,B);
    auto P2 = pickPointOutside(B,C);
    auto P3 = pickPointOutside(C,A);
    if (!(A.first == B.first || A.second == B.second))
        temp = temp - triangle(A,P1,B);
    if (!(B.first == C.first || B.second == C.second))
        temp = temp - triangle(B,P2,C);
    if (!(C.first == A.first || C.second == A.second))
        temp = temp - triangle(C,P3,A);
    return temp;
}

ld solveFast(vpii points) {
    moveToPositive(points);
    transpose(points);
    makeCounterClockwise(points);
    ld answ = 0;
    pii A(0,0);
    for (int i = 0; i < isz(points); i++) {
        pii B = points[i], C = points[(i+1)%isz(points)];
        ld curr = calcTriangle(A, B, C).first;
        if (rotation(A,B,C) == LEFT) answ += curr;
        else answ -= curr;
    }
    return answ;
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    std::cout << std::fixed << std::setprecision(12);
    auto points = readPolygon();
    std::cout << solveFast(points) << std::endl;
}