#include<bits/stdc++.h>

using namespace std;

int main(){
  vector<pair<long long,pair<int,int>>> vc;
  int n;
  cin >> n;
  vector<long long> a(n),b(n);
  for(int i=0;i<n;i++){
    cin >> a[i] >> b[i];
  }
  for(int i=0;i<n;i++){
    for(int j=i+1;j<n;j++){
      long long cost=0;
      cost+=(a[i]-a[j])*(a[i]-a[j]);
      cost+=(b[i]-b[j])*(b[i]-b[j]);
      vc.push_back(make_pair(cost,make_pair(i,j)));
    }
  }
  sort(vc.begin(),vc.end());
  int cnt=vc.size(),res=0;
  vector<int> fl(n,0);
  for(int i=0;i<cnt;i++){
    pair<int,int> conf=vc[i].second;
    int p=conf.first,q=conf.second;
    if(fl[p]==1 || fl[q]==1){continue;}
    //cout << p << q << '\n';
    if(p==0){res++;fl[q]=1;continue;}
    fl[p]=1;fl[q]=1;
  }
  cout << res << '\n';
  return 0;
}