#include <bits/stdc++.h>
using namespace std;

using Int = long long;
const char newl = '\n';

template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
template<typename T> void drop(const T &x){cout<<x<<endl;exit(0);}
template<typename T=Int>
vector<T> read(size_t n){
  vector<T> ts(n);
  for(size_t i=0;i<n;i++) cin>>ts[i];
  return ts;
}

//INSERT ABOVE HERE
signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);

  Int n;
  cin>>n;

  using D = Int;
  vector<D> xs(n),ys(n);
  for(Int i=0;i<n;i++) cin>>xs[i]>>ys[i];

  using T = tuple<D, Int, Int>;
  vector<T> vt;
  for(Int i=0;i<n;i++)
    for(Int j=0;j<i;j++)
      vt.emplace_back((xs[i]-xs[j])*(xs[i]-xs[j])+
                      (ys[i]-ys[j])*(ys[i]-ys[j]),i,j);

  sort(vt.begin(),vt.end());

  Int ans=0;
  vector<Int> alive(n,1);
  for(auto[d,i,j]:vt){
    if(!(alive[i] and alive[j])) continue;
    if(min(i,j)==0) ans++;
    alive[i]=alive[j]=0;
    alive[0]=1;
  }

  cout<<ans<<newl;
  return 0;
}