#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using T = tuple<ll, int, int>;

constexpr char newl = '\n';

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n;
    cin >> n;

    vector<ll> x(n), y(n);
    for (int i = 0; i < n; i++) {
        cin >> x[i] >> y[i];
    }

    priority_queue<T, vector<T>, greater<T> > pq;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < i; j++) {
            ll dx = x[i] - x[j], dy = y[i] - y[j];
            pq.emplace(dx * dx + dy * dy, j, i);
        }
    }

    vector<int> used(n, false);
    int ans = 0;
    int rest = n - 1;
    while (!pq.empty() && rest) {
        ll dist;
        int i, j;
        tie(dist, i, j) = pq.top();
        pq.pop();

        if (i == 0) {
            if (used[j]) continue;
            ++ans;
            used[j] = true;
            --rest;
        } else {
            if (used[i] || used[j]) continue;
            used[i] = true;
            used[j] = true;
            rest -= 2;
        }
    }
    cout << ans << newl;

    return 0;
}