signed main() {
    ios::sync_with_stdio(0), cin.tie(0);
    int n; cin >> n;
    vector<vector<int>> g(2001);
    vector<pair<int, int>> a(n);
    for (int i = 0; i < n; i++) {
        int u, v;
        cin >> u >> v;
        a[i].first = u + 1000;
        a[i].second = v + 1000;
        g[u + 1000].push_back(v + 1000);
        g[v + 1000].push_back(u + 1000);
    }
    int ans = 0;
    for (int i = 0; i < n; i++) {
        int x = a[i].first;
        int y = a[i].second;
        bool l = 0, r = 0, u = 0, d = 0;
        for (auto k : g[y]) {
            if (k > x) {
                r = 1;
            } else if (k < x) {
                l = 1;
            }       
        }
        for (auto k : g[x]) {
            if (k > y) {
                u = 1;
            } else if (k < y) {
                d = 1;
            }
        }
        if (l == 1 and r == 1 and u == 1 and d == 1) {
            ans += 1;
        }
    }
    std::cout << ans << "\n";
    return 0;
}