#include<iostream>
#include<vector>
#include<cmath>
#include<cstdio>
#include<algorithm>
#define EPS 1e-10
using namespace std;

struct P {
  double x,y;
  P(){}
  P(double x,double y):x(x),y(y){

  }

  P operator - (P p){
    return P(x-p.x,y-p.y);
  }

  double det(P p){
    return x*p.y-y*p.x;
  }

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

vector<P> totu(P* ps,int n){
  sort(ps,ps+n,comp);
  int k=0;
  vector<P> qs(n*2);
  for(int i=0;i<n;i++){
    while(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--){
    while(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;

  while(
	cin >> n 
	&& 
	n 
	)
    {
      P ps[n+1];
      for(int i=0;i<n;i++){
	scanf("%lf,%lf",&ps[i].x,&ps[i].y);
      }
      cout << n-totu(ps,n).size() << endl;
      
    }
  
  return 0;
}