#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
typedef vector <int> vi;
typedef pair<double,double> pd;
typedef vector <pd > vp;
vp D;
vi A;

int side(pd p1, pd p2){
	double dy=p2.first-p1.first,dx=p2.second-p1.second;
	for(int i=0;i<(int)D.size();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 n,i,s;
		pd p,p1,p2;
		char c;
		cin>>n;
		if (n==0) break;
		for (i=0;i<n;i++){
			cin>>p.first>>c>>p.second;
			D.push_back(p);
			A.push_back(0);
		}
		sort(D.begin(),D.end());
		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;
		}
		cout<<D.size()-s<<"\n";
		D.clear();
		A.clear();
	}
}