#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

struct ST {
  ll t2;
  int i, j;
};
bool operator<(const ST& a, const ST& b){
  return a.t2 > b.t2;
}


int main(){
  int N;
  cin >> N;
  vector<pair<ll,ll>> v;
  rep(i,N){
    ll x, y;
    cin >> x >> y;
    v.emplace_back(x,y);
  }

  priority_queue<ST> que;
  rep(i,N){
    REP(j,i+1,N){
      ll t2 = (v[i].first-v[j].first)*(v[i].first-v[j].first) +
        (v[i].second-v[j].second)*(v[i].second-v[j].second);
      que.push((ST){t2,i,j});
    }
  }

  int ret = 0;
  vector<bool> enable(N, true);
  while(!que.empty()){
    ST st = que.top(); que.pop();
    
    if(st.i == 0){
      if(enable[st.j]){
        ret++;
        enable[st.j] = false;
      }
    } else {
      if(enable[st.i] && enable[st.j]){
        enable[st.i] = false;
        enable[st.j] = false;
      }
    }
  }

  cout << ret << endl;
  
  return 0;
}