#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<deque>
#include<map>
#include<set>
#include<string>
#include<sstream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<cctype>
#include<complex>
#include<climits>
#include<complex>
#define REP(i, j) for(int i = 0; i < j; i++)
#define FOR(i, j, k) for(int i = j; i < k; i++)
using namespace std;
typedef complex<double> P;
typedef vector<P> G;
const double EPS = 1e-8;
const double INF = 1e12;
namespace std {
    bool operator < (const P& a, const P& b) {
        return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
    }
}
double cross(const P& a, const P& b) {
    return imag(conj(a)*b);
}
double dot(const P& a, const P& b) {
    return real(conj(a)*b);
}
int ccw(P a, P b, P c) {
    b -= a; c -= a;
    if (cross(b, c) > 0)   return +1;       // counter clockwise
    if (cross(b, c) < 0)   return -1;       // clockwise
    if (dot(b, c) < 0)     return +2;       // c--a--b on line
    if (norm(b) < norm(c)) return -2;       // a--b--c on line
    return 0;
}


G convex_hull(G &ps) {
  int n = ps.size(), k = 0;
  sort(ps.begin(), ps.end());
  G ch(2*n);
  for (int i = 0; i < n; ch[k++] = ps[i++]) // lower-hull
    while (k >= 2 && ccw(ch[k-2], ch[k-1], ps[i]) == -1) --k;
  for (int i = n-2, t = k+1; i >= 0; ch[k++] = ps[i--]) // upper-hull
    while (k >= t && ccw(ch[k-2], ch[k-1], ps[i]) == -1) --k;
  ch.resize(k-1);
  return ch;
}

int main(){
  int N;
  while(cin >>N && N){
    G ps(N);
    REP(i, N){
      double x, y;
      scanf("%lf,%lf", &x, &y);
      ps[i] = P(x, y);
    }
    G res = convex_hull(ps);
    cout <<N - (int)(res.size()) <<endl;
  }
  return 0;
}