#include <algorithm>
#include <iostream>
using namespace std;
typedef pair<double,double> pd;

pd D[100];
int A[100];
int n;

int side(pd p1, pd p2){
	double dy=p2.first-p1.first,dx=p2.second-p1.second;
	for(int i=0;i<n;i++){
		pd p3=D[i];
		if (p1==p3||p2==p3)continue;
		if ((p3.second-p1.second)*dy-dx*(p3.first-p1.first)<0) return 0;
	}
    return 1;
}

int main(){
	while (1){
		int i,s;
		pd p,p1,p2;
		char c;
		cin>>n;
		if (n==0) break;
		for (i=0;i<n;i++){
			cin>>D[i].first>>c>>D[i].second;
			A[i]=0;
		}
		sort(D,D+n);
		p=D[0];
		p1=p;
		s=0;
		while (1){
			for (i=0;i<n;i++){
				p2=D[i];
				if (A[i]==0 && p1!=p2 && side(p1,p2)) break;
			}
			p1=p2;
			A[i]=1;
			s++;
			if (p2==p) break;
		}
		std::cout<<n-s<<"\n";
		for (i=0;i<n;i++){
			D[i]=make_pair(0,0);
			A[i]=0;
		}
	}
}