#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define rep(i,n) for(int i=0;i<(n);i++)
#define pll pair<ll,ll>
#define pii pair<int,int>
#define pq priority_queue
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define endl '\n'
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define lb(c,x) distance(c.begin(),lower_bound(all(c),x))
#define ub(c,x) distance(c.begin(),upper_bound(all(c),x))

using namespace std;

const ll INF=1e9+10;

int main(){
    ll n;
    cin >> n;
    vector<ll> x(n),y(n);
    rep(i,n){
        cin >> x[i] >> y[i];
    }
    priority_queue<pair<ll,pll>> PQ;
    vector<ll> used(n);
    ll ans=0;
    rep(i,n){
        for(ll j=i+1;j<n;j++){
            ll dx=abs(x[i]-x[j]),dy=abs(y[i]-y[j]);
            ll d=dx*dx+dy*dy;
            pair<ll,pll> x;
            x.fi=-d;
            x.se.fi=i,x.se.se=j;
            PQ.push(x);
        }
    }
    while(!PQ.empty()){
        pair<ll,pll> x;
        x=PQ.top();
        PQ.pop();
        if(used[x.se.fi] || used[x.se.se]) continue;
        if(x.se.fi==0){
            ans++;
            used[x.se.se]=1;
        }
        else{
            used[x.se.fi]=1,used[x.se.se]=1;
            
        }
    }
    cout << ans << endl;
    return 0;
}