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

struct P{
	double x, y;
	P(){}
	P(double x, double y) : x(x), y(y) {
	}
	P operator - (P p) {
		return P(x-p.x,y-p.y);
	}
	double det(P p){
		return x*p.y-y*p.x;
	}
	bool operator<(const P& r) const {
		return x==r.x?y<r.y:x<r.x;
	}
};

int n;
P p[100];

void solve(){
	int k = 0;
	char tra;
	rep(i,n) scanf("%lf%c%lf", &p[i].x, &tra, &p[i].y);
	sort(p,p+n);
	P qs[200];
	rep(i,n){
		while(k > 1 && (qs[k-1]-qs[k-2]).det(p[i]-qs[k-1]) <= 0) k--;
		qs[k++] = p[i];
	}
	for(int i = n-2, t = k; i >= 0; i--){
		while(k > t && (qs[k-1]-qs[k-2]).det(p[i]-qs[k-1]) <= 0) k--;
		qs[k++] = p[i];
	}
	printf("%d\n",n-k+1); 
}

int main(){
	while(scanf("%d",&n),n) solve();
}