#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#include <queue>
#include <tuple>

using namespace std;
using ll=long long;

int main(){
    ll n,ans=0;
    cin>>n;
    vector<ll> x(n),y(n),kil(n,0);
    priority_queue<tuple<ll,ll,ll>,vector<tuple<ll,ll,ll>>,greater<tuple<ll,ll,ll>>> q;

    for(ll i=0;i<n;i++) cin>>x[i]>>y[i];
    
    for(ll i=0;i<n;i++){
        for(ll j=i+1;j<n;j++){
            ll xi,yi,xj,yj;
            xi=x[i],yi=y[i],xj=x[j],yj=y[j];
            q.push(make_tuple(powl(xi-xj,2)+powl(yi-yj,2),i,j));
        }
    }
    while(q.size()){
        ll d,i,j;
        tie(d,i,j)=q.top();q.pop();
        if(kil[i]||kil[j]) continue;
        if(i!=0&&j!=0){
            kil[i]=1;
            kil[j]=1;
        }else{
            kil[j]=1;
            ans++;
        }
    }
    cout<<ans<<endl;
    return 0;
}