#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>

using namespace std;

#define EPS 1e-10

double add(double a,double b){
  if(abs(a+b) < EPS*(abs(a)+abs(b)))return 0;
  return a+b;
}

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

  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));
  }

  P operator * (double d){
    return P(x*d,y*d);
  }

  double dot(P p){
    return add(x*p.x,y*p.y);
  }
  double det(P p){
    return add(x*p.y,-y*p.x);
  }
};
bool cmp_x(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(vector<P> ps , int N)
{
  sort(ps.begin(),ps.end(),cmp_x);
  /*for(int i = 0 ; i < N ; i++ ){
    cout << ps[i].x << ' ' << ps[i].y << endl;
    }*/
  vector<P> qs(N*2);
  int k = 0;
  for(int i = 0 ; i < (int)ps.size() ; 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){
    vector<P> ps(n);
    char c;
    for(int i = 0 ; i < n ; i++ ){
      cin >> ps[i].x >>c>> ps[i].y;
    }
    vector<P> qs = convex_hull(ps, n);
    cout << ps.size()-qs.size() << endl;
  }
  return 0;
}