struct PredProblem
{
    static constexpr int B = 64;
    uint64_t tree[32];
    int treeID;
    PredProblem()
    {
        for (auto &i : tree)
            i = -1;
        treeID = -1;
    };
    void erase(const int i)
    {
        tree[i / B] &= ~(1ULL << (i % B));
        if (!tree[i / B])
            treeID &= ~(1 << (i / B));
    };
    bool get(const int i)
    {
        return tree[i / B] & (1ULL << (i % B));
    };
    int next(const int i)
    {
        uint64_t a = tree[i / B] & -(1ULL << (i % B));
        if (!a)
        {
            int nb = __builtin_ctz(treeID & -(1 << (i / B + 1)));
            return nb * B + __builtin_ctzll(tree[nb]);
        }
        else
            return i / B * B + __builtin_ctzll(a);
    };
    int prev(const int i)
    {
        uint64_t a = tree[i / B] & ((i % B == 63 ? 0 : (1ULL << (i % B + 1))) - 1);
        if (!a)
        {
            int x = treeID & ((1 << (i / B)) - 1);
            if (!x)
                return -1;
            int nb = __lg(x);
            return nb * B + __lg(tree[nb]);
        }
        else
            return i / B * B + __lg(a);
    };
};