#include <bits/stdc++.h>
using namespace std;
#include <math.h>
#include <iomanip>
#include <cstdint>
#define rep(i,n) for (int i = 0; i < (n); ++i)
using ll = long long;
using P = pair<int,int>;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const int INF=1001001001;
const int mod=1000000007;

int main() {
  int N;
  cin>>N;
  vector<int>x(N),y(N);
  for(int i=0;i<N;i++){
    cin>>x[i]>>y[i];
  }
  priority_queue<pair<int64_t,pair<int,int>>>q;
  for(int i=0;i<N;i++){
    for(int j=i+1;j<N;j++){
      int64_t dx=x[j]-x[i],dy=y[j]-y[i];
      int64_t dis=dx*dx+dy*dy;
      q.push(make_pair(-dis,make_pair(i,j)));
    }
  }
  vector<bool>seen(N,false);
  int cnt=0;
  while(!q.empty()){
    int d=q.top().first,i=q.top().second.first,j=q.top().second.second;
    q.pop();
    if(i==0||j==0){
      if(!seen[i+j-0]){cnt++;seen[i+j-0]=true;}//i+j-0=0の相方
    }
    else if(!seen[i]&&!seen[j]){seen[i]=true;seen[j]=true;}
  }
  cout<<cnt<<endl;
  return 0;
}