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

ll gcd(ll a, ll b) {
	return (a ? gcd(b % a, a) : b);
}
int main () {
	int N;
	cin >> N;
	ll X[2020], Y[2020];
	for (int i = 0; i < N; i ++) cin >> X[i] >> Y[i];
	int ans = 0;
	using P = pair<ll, ll>;
	P A[2020];
	for (int i = 0; i < N; i ++) {
		for (int j = 1; j < N; j ++) {
			int k = (i + j) % N;
			ll dx = X[k] - X[i], dy = Y[k] - Y[i];
			ll g = gcd(abs(dx), abs(dy));
			A[j - 1] = P{dx / g, dy / g};
		}
		sort(A, A + (N - 1));
		for (int j = 0; j < N - 2; j ++) {
			if (A[j] == A[j + 1]) {
				ans ++;
				break;
			}
		}
	}
	cout << ans << endl;
}