#include<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;
typedef pair<double, double>P;

P p[100];
double det(P a, P b) {
	return a.first*b.second - a.second*b.first;
}
P operator-(P a, P b) { return P(a.first - b.first, a.second - b.second); }
int main() {
	int n;
	while (scanf("%d", &n), n) {
		rep(i, n)scanf("%lf,%lf", &p[i].first, &p[i].second);
		sort(p, p + n);
		vector<P>a(n * 2);
		int k = 0;
		rep(i, n) {
			while (k > 1 && det(a[k - 1] - a[k - 2], p[i] - a[k - 2]) < 0)k--;
			a[k++] = p[i];
		}
		for (int i = n - 2; i >= 0; i--) {
			while (k > 1 && det(a[k - 1] - a[k - 2], p[i] - a[k - 2]) < 0)k--;
			a[k++] = p[i];
		}
		printf("%d\n", n - k + 1);
	}
}