#include <cstdio>
#include <complex>
#include <algorithm>
using namespace std;
bool cmp(complex<double> a,complex<double> b){
  if(a.real()!=b.real()) return a.real()<b.real();
  return a.imag()<b.imag();
}
int main(){
  int n;
  while(1){
    scanf("%d",&n);
    if(n==0) return 0;
    complex<double> p[n];
    for(int i=0;i<n;++i){
      scanf("%lf,%lf",&p[i].real(),&p[i].imag());
    }
    sort(p,p+n,cmp);
    int k=0;
    complex<double> q[n*2];
    for(int i=0;i<n;i++){
      if(k>1&&arg(q[k-1]-q[k-2])>arg(p[i]-q[k-1])) k--;
      q[k++]=p[i];
    }
    for(int i=n-2,t=k;i>=0;i--){
      if(k>t&&arg(q[k-1]-q[k-2])<arg(p[i]-q[k-1])) k--;
      q[k++]=p[i];
    }
    printf("%d\n",n-k+1);
  }
  return 0;
}