#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const double pi = 3.141592653589793;
typedef unsigned long long ull;
typedef long double ldouble;
const ll INF = 1e18;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define rep2(i, s, n) for (ll i = (s); i < (ll)(n); i++)
template <class T>
inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}
typedef pair<int, int> P;
typedef pair<ll, ll> PL;

ll dis (pair<ll, ll> a, pair<ll, ll> b) {
    return (ll)(a.first - b.first) * (ll)(a.first - b.first) + (ll)(a.second - b.second) * (ll)(a.second - b.second);
}

int main() {
    ll n;
    cin >> n;
    vector<P> xy(n);
    rep(i, n) {
        cin >> xy[i].first >> xy[i].second;
    }
    vector<pair<int, pair<int , int> > > kn;
    vector<bool> used(n, false);
    rep2(i, 0, n-1) {
        ll this_dis = INF, ind = -1;
        rep2(j, i+1, n) {
            if(i == j) continue;
            ll dis_y = dis(xy[i], xy[j]);
            pair<int, pair<int, int> > k;
            k.first = floor(sqrt(dis_y) + 0.999999999);
            k.second.first = i;
            k.second.second = j;
            kn.emplace_back(k);
        }
    }
    sort(kn.begin(), kn.end());
    int ans = 0;
    rep(i, kn.size()) {
        int a = kn[i].second.first;
        int b = kn[i].second.second;
        if(used[a] == false && used[b] == false ) {
            // cout << kn[i].first << " a:" << a << " b:" << b << endl;
            if(a == 0) {
                used[b] = true;
                ans++;
            }
            else if(b == 0) {
                used[a] = true;
                ans++;
            }
            else {
                used[a] = true;
                used[b] = true;
            }
        }
    }

    cout << ans << endl;
}