#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<algorithm>
#include<vector>
#include<string.h>
#include<math.h>
#include<map>
#include<iomanip>
#include<queue>
#include<set>

#define rep(i,n) for(int (i) = 0; i < (n); i++)

using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;

//const ll mod = 1e9 + 7;
const ll mod = 998244353;
const int inf = 123456;
const int siz = 202020;

ll dist(int a , int b , int c , int d){
    return (ll)(a - b)*(a - b) + (ll)(c - d)*(c - d);
}

int main() {
        int n;
        cin >> n;
        vector<int> x(n) , y(n);
        for(int i = 0; i < n; i++){
            cin >> x[i] >> y[i];
        }
        vector<pair<ll , pair<int , int> > > v;
        for(int i = 0; i < n - 1; i++){
            for(int j = i + 1; j < n; j++){
                ll d = dist(x[i] , x[j] , y[i] , y[j]);
                v.push_back(make_pair(d , make_pair(i , j)));
            }
        }
        sort(v.begin() , v.end());
        vector<bool> used(n + 100 , false);
        int ans = 0;
        for(int i = 0; i < v.size(); i++){
            int x = v[i].second.first;
            int y = v[i].second.second;
            if(used[x] == false && used[y] == false){
            	if(x == 0){
            		ans++;
            		used[y] = true;
            	}else{
            		used[x] = used[y] = true;
            	}
            }
        }
        cout << ans << endl;
    return 0;
}