#include<iostream>
#include<cstdio>
#include<vector>
#include<algorithm>
#include<map>
using namespace std;
int main(){
  int n;
  while(cin >>n,n){
    vector<pair<double,double> > dot;
    bool f[100]={false};
    for(double i=0,a,b; i<n; i++){scanf("%lf,%lf",&a,&b);dot.push_back(make_pair(a,b));}
    sort(dot.begin(),dot.end());
    int now=0,next;
    for(;;){
      for(int i=0; i<n; i++){
	if(i!=now && !f[i]){
	  next = i;
	  double ax=dot[i].first-dot[now].first;
	  double ay=dot[i].second-dot[now].second;
	  for(int j=0; j<n; j++){
	    if(!f[j]){
	      double bx=dot[j].first-dot[now].first;
	      double by=dot[j].second-dot[now].second;
	      if(ax*by-ay*bx<0){next = -1;break;}
	    }
	  }
	  if(next == i) break;
	}
      }
      f[next] = true;
      now = next;
      if(f[0]) break;
    }
    int ans = 0;
    for(int i=0; i<n; i++) if(!f[i]) ans++;
    cout <<ans<<endl;
  }
  return 0;
}