#include <iostream>
#include <vector>
#include <queue>
#include <tuple>
using namespace std;
typedef tuple<long long, int, int> P;
#define g(a, t) get<t>(a)
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    vector<long long> x(N), y(N);
    for(int i = 0; i < N; i++) cin >> x[i] >> y[i];
    priority_queue<P, vector<P>, greater<P>> q;
    for(int i = 0; i < N; i++){
        for(int j = i + 1; j < N; j++){
            long long temp = (x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j]);
            q.push(P(temp, i, j));
        }
    }
    vector<int> used(N);
    int cnt = 0;
    while(!q.empty()){
        P t = q.top();
        q.pop();
        int s1 = g(t, 1), s2 = g(t, 2);
        if(used[s1] == 1 || used[s2] == 1) continue;
        else if(s1 == 0){
            used[s2] = 1;
            cnt++;
        }
        else if(s2 == 0){
            used[s1] = 1;
            cnt++;
        }
        else{
            used[s1] = 1;
            used[s2] = 1;
        }
    }
    cout << cnt << endl;
}