//11
#include<iostream>
#include<complex>
#include<algorithm>
#include<vector>

using namespace std;

typedef complex<double> P;

double det(P a,P b){
  return a.real()*b.imag()-a.imag()*b.real();
}

bool cmp(P a,P b){
  if(a.real()!=b.real()){
    return a.real()<b.real();
  }else{
    return a.imag()<b.imag();
  }
}

int main(){
  for(int n;cin>>n,n;){
    P ps[100];
    for(int i=0;i<n;i++){
      double x,y;
      (cin>>x).ignore()>>y;
      ps[i]=P(x,y);
    }
    sort(ps,ps+n,cmp);
    int k=0;
    vector<P> qs(n*2);
    for(int i=0;i<n;i++){
      while(k>1&&det(qs[k-1]-qs[k-2],ps[i]-qs[k-1])<=0)k--;
      qs[k++]=ps[i];
    }
    for(int i=n-2,t=k;i>=0;i--){
      while(k>t&&det(qs[k-1]-qs[k-2],ps[i]-qs[k-1])<=0)k--;
      qs[k++]=ps[i];
    }
    cout<<n-(k-1)<<endl;
  }
  return 0;
}
    