// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h> 
using namespace std;
typedef long long ll;
#define endl '\n'
#define all(x) (x).begin(),(x).end()
template<typename T1,typename T2> bool chmin(T1 &a,T2 b){if(a<=b)return 0; a=b; return 1;}
template<typename T1,typename T2> bool chmax(T1 &a,T2 b){if(a>=b)return 0; a=b; return 1;}
int dx[4]={0,1,0,-1}, dy[4]={1,0,-1,0};
long double eps = 1e-9;
long double pi = acos(-1);

struct S{
    ll time;
    int l,r;
    bool operator>(const S &s) const{
        return time > s.time;
    }
};

signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(20);

    int n;
    cin>>n;
    ll x[n],y[n];
    for(int i=0;i<n;i++){
        cin>>x[i]>>y[i];
    }
    int ans = 0;
    bool used[n]={};
    priority_queue<S,vector<S>,greater<S>> pq;
    for(int i=0;i<n;i++){
        for(int j=i+1;j<n;j++){
            ll dist = (x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j]);
            pq.push({dist,i,j});
        }
    }
    while(pq.size()){
        auto [time,l,r] = pq.top();
        pq.pop();
        if(used[l] || used[r])continue;
        if(l!=0)used[l] = 1;
        used[r] = 1;
        if(l == 0)ans++;
    }
    cout << ans << endl;



}