#include <iostream>
#include <cstdio>
#include <utility>
#include <vector>
#include <algorithm>

using namespace std;
#define rep2(x,from,to) for(int x = (from); x < (to); ++(x))
#define rep(x,to) rep2(x,0,to)
typedef pair<double, double> dpair;

double det(dpair p1, dpair p2, dpair p3) {
	return (p2.first - p1.first) * (p3.second - p2.second) - (p2.second - p1.second) * (p3.first - p2.first);
}
int main() {
	int n;
	while(cin >> n && n) {
		vector<dpair> v;
		rep(i,n) {
			double x, y;
			scanf("%lf,%lf", &x, &y);
			v.push_back(make_pair(x,y));
		}
		sort(v.begin(), v.end());
		dpair conv[205];
		int k = 0;
		rep(i,n) {
			while(k > 1 && det(conv[k-2], conv[k-1], v[i]) <= 0) --k;
			conv[k++] = v[i];
		}
		for(int i = n - 2, t = k; i >= 0; --i) {
			while(k > t && det(conv[k-2], conv[k-1], v[i]) <= 0) --k;
			conv[k++] = v[i];
		}
		cout << n - k + 1 << endl;
	}
	return 0;
}