#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <algorithm>
#include <utility>
#define rep(x, s, t) for(llint (x) = (s); (x) <= (t); (x)++)
#define chmin(x, y) (x) = min((x), (y))
#define chmax(x, y) (x) = max((x), (y))
#define all(x) (x).begin(),(x).end()
#define inf 1e18

using namespace std;

typedef long long llint;
typedef pair<llint, llint> P;
typedef pair<llint, P> T;

llint n;
priority_queue<T, vector<T>, greater<T> > Q;
llint x[1005], y[1005];
bool used[1005];

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n;
	for(int i = 1; i <= n; i++) cin >> x[i] >> y[i];
	
	for(int i = 1; i <= n; i++){
		for(int j = 1; j <= n; j++){
			if(i >= j) continue;
			Q.push(T((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]), P(i, j)));
		}
	}
	
	llint ans = 0;
	while(Q.size()){
		llint x = Q.top().second.first, y = Q.top().second.second;
		Q.pop();
		if(used[x] || used[y]) continue;
		if(x == 1 || y == 1) ans++;
		if(x != 1) used[x] = true;
		if(y != 1) used[y] = true;
	}
	cout << ans << endl;
	
	return 0;
}