#include "bits/stdc++.h"
using namespace std;
//#include "atcoder/all"
//using namespace atcoder;
#define int long long
#define REP(i, n) for (int i = 0; i < (int)n; ++i)
#define RREP(i, n) for (int i = (int)n - 1; i >= 0; --i)
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define RFOR(i, s, n) for (int i = (int)n - 1; i >= s; --i)
#define ALL(a) a.begin(), a.end()
#define IN(a, x, b) (a <= x && x < b)
template<class T>istream&operator >>(istream&is,vector<T>&vec){for(T&x:vec)is>>x;return is;}
template<class T>inline void out(T t){cout << t << "\n";}
template<class T,class... Ts>inline void out(T t,Ts... ts){cout << t << " ";out(ts...);}
template<class T>inline bool CHMIN(T&a,T b){if(a > b){a = b;return true;}return false;}
template<class T>inline bool CHMAX(T&a,T b){if(a < b){a = b;return true;}return false;}
constexpr int INF = 1e18;



signed main(){
	int N;
	cin >> N;
	int ans = 0;
	set<tuple<int, int, int>>st;
	vector<int> x(N), y(N);
	REP(i, N) cin >> x[i] >> y[i];
	auto cost = [&](int i, int j) -> int {
		return (x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j]);
	};
	REP(i, N) {
		REP(j, N) {
			if(i == j) continue;
			st.insert({cost(i, j), i, j});
		}
	}
	int n = N;
	vector<int> erased(N);
	while(n > 1) {
		int dist, a, b;
		while(1) {
			tie(dist, a, b) = *st.begin();
			if(erased[a] == 0 && erased[b] == 0) break;
			else st.erase(st.begin());
		}
		st.erase(st.begin());
		if(a > b) swap(a, b); // a < b
		if(a == 0) {
			erased[b] = 1;
			++ans;
			--n;
		} else {
			erased[a] = erased[b] = 1;
			--n;--n;
		}
	}
	out(ans);
}