#include "bits/stdc++.h"
using namespace std;
using     ll=long long;
using    vll=vector<   ll>;
using   vvll=vector<  vll>;
using  vvvll=vector< vvll>;
using vvvvll=vector<vvvll>;
using     dd=double;
using    vdd=vector<   dd>;
using   vvdd=vector<  vdd>;
using pll=pair<ll,ll>; using tll=tuple<ll,ll,ll>; using qll=tuple<ll,ll,ll,ll>;
using   vpll=vector<  pll>;

constexpr ll INF = 1LL << 60;
struct Fast{ Fast(){ cin.tie(0); ios::sync_with_stdio(false); cout<<fixed<<setprecision(numeric_limits<double>::max_digits10); } } fast;
#define REPS(i, S, E) for (ll i = (S); i <= (E); i++)
#define REP(i, N) REPS(i, 0, (N)-1)
#define DEPS(i, S, E) for (ll i = (E); i >= (S); i--)
#define DEP(i, N) DEPS(i, 0, (N)-1)
#define rep(i, S, E)  for (ll i = (S); i <= (E); i++)
#define dep(i, E, S)  for (ll i = (E); i >= (S); i--)
#define each(e, v) for (auto&& e : v)
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
template<class T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; }return false; }
template<class T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; }return false; }
template<class T> inline T MaxE(vector<T>&v,ll S,ll E){ T m=v[S]; rep(i,S,E)chmax(m,v[i]); return m; }
template<class T> inline T MinE(vector<T>&v,ll S,ll E){ T m=v[S]; rep(i,S,E)chmin(m,v[i]); return m; }
template<class T> inline T MaxE(vector<T> &v) { return MaxE(v,0,(ll)v.size()-1); }
template<class T> inline T MinE(vector<T> &v) { return MinE(v,0,(ll)v.size()-1); }
template<class T> inline T Sum(vector<T> &v,ll S,ll E){ T s=T(); rep(i,S,E)s+=v[i]; return s; }
template<class T> inline T Sum(vector<T> &v) { return Sum(v,0,v.size()-1); }
template<class T> inline ll sz(T &v){ return (ll)v.size(); }
inline ll CEIL(ll a,ll b){ return (a<0) ? -(-a/b) : (a+b-1)/b; }
inline ll FLOOR(ll a,ll b){ return -CEIL(-a,b); }


#if 0
#include <atcoder/all>
using namespace atcoder;
#endif

//tuple3用テンプレート
using  vtll=vector< tll>;
using vvtll=vector<vtll>;
template<class T,class S,class R> inline tuple<T,S,R>& operator+=(tuple<T,S,R> &a,const tuple<T,S,R> &b){ get<0>(a)+=get<0>(b); get<1>(a)+=get<1>(b); get<2>(a)+=get<2>(b); return a; }
template<class T,class S,class R> inline tuple<T,S,R>& operator-=(tuple<T,S,R> &a,const tuple<T,S,R> &b){ get<0>(a)-=get<0>(b); get<1>(a)-=get<1>(b); get<2>(a)-=get<2>(b); return a; }
template<class T,class S,class R> inline tuple<T,S,R>& operator*=(tuple<T,S,R> &a,const tuple<T,S,R> &b){ get<0>(a)*=get<0>(b); get<1>(a)*=get<1>(b); get<2>(a)*=get<2>(b); return a; }
template<class T,class S,class R> inline tuple<T,S,R>& operator/=(tuple<T,S,R> &a,const tuple<T,S,R> &b){ get<0>(a)/=get<0>(b); get<1>(a)/=get<1>(b); get<2>(a)/=get<2>(b); return a; }
template<class T,class S,class R> inline tuple<T,S,R>& operator%=(tuple<T,S,R> &a,const tuple<T,S,R> &b){ get<0>(a)%=get<0>(b); get<1>(a)%=get<1>(b); get<2>(a)%=get<2>(b); return a; }
template<class T,class S,class R,class Q> inline tuple<T,S,R>& operator+=(tuple<T,S,R> &a,Q b){ get<0>(a)+=b; get<1>(a)+=b; get<2>(a)+=b; return a; }
template<class T,class S,class R,class Q> inline tuple<T,S,R>& operator-=(tuple<T,S,R> &a,Q b){ get<0>(a)-=b; get<1>(a)-=b; get<2>(a)-=b; return a; }
template<class T,class S,class R,class Q> inline tuple<T,S,R>& operator*=(tuple<T,S,R> &a,Q b){ get<0>(a)*=b; get<1>(a)*=b; get<2>(a)*=b; return a; }
template<class T,class S,class R,class Q> inline tuple<T,S,R>& operator/=(tuple<T,S,R> &a,Q b){ get<0>(a)/=b; get<1>(a)/=b; get<2>(a)/=b; return a; }
template<class T,class S,class R,class Q> inline tuple<T,S,R>& operator%=(tuple<T,S,R> &a,Q b){ get<0>(a)%=b; get<1>(a)%=b; get<2>(a)%=b; return a; }
template<class T,class S,class R,class Q> inline tuple<T,S,R> operator+(const tuple<T,S,R> &a,Q b){ tuple<T,S,R> c=a; return c+=b; }
template<class T,class S,class R,class Q> inline tuple<T,S,R> operator-(const tuple<T,S,R> &a,Q b){ tuple<T,S,R> c=a; return c-=b; }
template<class T,class S,class R,class Q> inline tuple<T,S,R> operator*(const tuple<T,S,R> &a,Q b){ tuple<T,S,R> c=a; return c*=b; }
template<class T,class S,class R,class Q> inline tuple<T,S,R> operator/(const tuple<T,S,R> &a,Q b){ tuple<T,S,R> c=a; return c/=b; }
template<class T,class S,class R,class Q> inline tuple<T,S,R> operator%(const tuple<T,S,R> &a,Q b){ tuple<T,S,R> c=a; return c%=b; }
template<class T,class S,class R,class Q> inline tuple<T,S,R> operator-(Q b,const tuple<T,S,R> &a){ tuple<T,S,R> c=-a; return c+=b; }
template<class T,class S,class R> inline tuple<T,S,R> operator-(const tuple<T,S,R> &a){ tuple<T,S,R> c=a; return c*=(-1); }
template<class T,class S,class R> inline ostream &operator<<(ostream &os,const tuple<T,S,R> &a){ return os << get<0>(a) << ' ' << get<1>(a) << ' ' << get<2>(a); }


template<class T> inline T POW(T a,ll n){ T r=1; for (; n>0; n>>=1,a*=a){ if (n&1)r*=a; } return r; }
inline ll POW(int a,ll n){ return POW((ll)a,n); }

void solve()
{
	ll n;  cin >> n;
	vector<pair<ll,ll>> xy(n);
	rep(i,0,n-1){ ll x; ll y; cin>>x>>y; xy[i]={x,y}; }

	vtll ds;
	rep(i,0,n-1){
		rep(j,i+1,n-1){
			ll x,y;  tie(x,y) = xy[i];
			ll xx,yy;  tie(xx,yy) = xy[j];
			ds.emplace_back(POW(x-xx,2)+POW(y-yy,2),i,j);
		}
	}
	sort(ALL(ds));

	vll ans;
	unordered_set<ll> removed;
	each(e,ds){
		ll d,i,j;  tie(d,i,j) = e;

		/*
		どちらかが既にない→skip
		0とペア→ansとremovedにいれる
		それ以外→removedにいれる
		*/
		if (removed.count(i)==1 or removed.count(j)==1){
			continue;
		}
		if (i==0){
			ans.push_back(j);
			removed.insert(j);
		}
		else{
			removed.insert(i);
			removed.insert(j);
		}
	}
	cout << sz(ans) << '\n';

}

int main(){
#if 1
	solve();
#else
	ll t;  cin >> t;
	rep(i, 0, t-1){
		solve();
	}
#endif
	return 0;
}