#include<cstdio>
#include<cmath>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;
double EPS=1e-10;
struct P{
	double x,y;
	P(){};
	P(double x,double y):x(x),y(y){};
	double add(double a,double b){if(abs(a+b)<EPS*(abs(a)+abs(b)))return 0;return a+b;}
	P operator +(P p){return P(add(x,p.x),add(y,p.y));}
	P operator -(P p){return P(add(x,-p.x),add(y,-p.y));}
	double dot(P p){return add(x*p.x,y*p.y);}
	double det(P p){return add(x*p.y,-y*p.x);}
};

P pos[105];

bool cmp_p(const P &p,const P&q)
{
	if(p.x!=q.x)return p.x<q.x;
	return p.y<q.y;
}

vector<P> convex_hull(P *ps,int n)
{
	sort(ps,ps+n,cmp_p);
	int k=0;
	vector<P> qs(n*n);
	for(int i=0;i<n;i++)
	{
		for(;k>1&&(qs[k-1]-qs[k-2]).det(ps[i]-qs[k-1])<=0;)k--;
		qs[k++]=ps[i];
	}
	for(int i=n-2,t=k;i>=0;i--)
	{
		for(;k>t&&(qs[k-1]-qs[k-2]).det(ps[i]-qs[k-1])<=0;)k--;
		qs[k++]=ps[i];
	}
	qs.resize(k-1);
	return qs;
}

int main()
{
	int N;
	for(;scanf("%d",&N),N;)
	{
		memset(pos,0,sizeof(pos));
		for(int i=0;i<N;i++)
			scanf("%lf,%lf",&pos[i].x,&pos[i].y);
		printf("%d\n",N-convex_hull(pos,N).size());
	}
}