#include <bits/stdc++.h>
using namespace std;
template <typename T> using vec = vector<T>;
template <typename T> using vvec = vector<vector<T>>;

int main() {
    int n; cin >> n;
    vec<array<int, 2>> bal(n);
    for (auto &[x, y]: bal) cin >> x >> y;

    using dist_t = array<int64_t, 3>;
    priority_queue<dist_t, vector<dist_t>, greater<dist_t>> que;
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j < n; ++j) {
            int64_t dx = abs(bal[i][0] - bal[j][0]), dy = abs(bal[i][1] - bal[j][1]);
            que.push({ dx * dx + dy * dy , i, j });
        }
    }

    int ans = 0;

    vec<bool> used(n, false);
    while (que.size()) {
        auto [d, a, b] = que.top(); que.pop();
        if (used[a] || used[b]) continue;

        tie(a, b) = make_tuple(min(a, b), max(a, b));
        used[a] = a != 0;
        used[b] = true;

        ans += a == 0;
    }

    cout << ans << endl;
}