#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main(){
	for(;;){
		int n;
		cin >>n;
		if(!n){break;}
		double pin[100][2] = {0},min_x =  10000;
		int rubber[2] = {0};
		bool done[100] = {false};
		for(int i=0; i<n; i++){
			scanf("%lf,%lf",&pin[i][0],&pin[i][1]);
			if(min_x>pin[i][0]){min_x = pin[i][0];rubber[0] = i;}
		}
		rubber[1] = rubber[0];
		for(;;){
			int now,j;
			for(int i=0; i<n; i++){
				if(!done[i] && i!=rubber[1]){
					double ax = pin[i][0]-pin[rubber[1]][0];
					double ay = pin[i][1]-pin[rubber[1]][1];
					for(j=0; j<n; j++){
						if(!done[j]){
							double bx = pin[j][0]-pin[rubber[1]][0];
							double by = pin[j][1]-pin[rubber[1]][1];
							if(ax*by-ay*bx<0){break;}
						}
					}
					if(j == n){now = i;break;}
				}
			}
			done[now] = true;
			rubber[1] = now;
			if(rubber[1] == rubber[0]){break;}
		}
		int sum = 0;
		for(int i=0; i<n; i++){if(!done[i]){sum++;}}
		cout <<sum<<endl;
	}
	return 0;
}