#include "bits/stdc++.h"
#include<string>
#include<sstream>
using namespace std;
typedef complex<double> P;

const double eps = 1e-8;

namespace std {
  bool operator <(const P &a, const P &b) {
    if(a.real() != b.real()) return a.real() < b.real();
    return a.imag() < b.imag();
  }
}

double dot(P a, P b) {
  return a.real()*b.real() + a.imag()*b.imag();
}

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

int ccw(P p, P a, P b) {
  a -= p;
  b -= p;
  if(cross(a,b) > eps) return 1;
  if(cross(a,b) < -eps) return -1;
  if(dot(a,b) < -eps) return 2;
  if(norm(b)-norm(a) > eps) return -2;
  return 0;
}

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

int main() {
  int n;
  while(scanf("%d", &n) != EOF && n) {
    vector<P> g(n);
    for(int i = 0; i < n; ++i) {
      P &p = g[i];
      scanf("%lf,%lf", &p.real(), &p.imag());
    }
    printf("%d\n", g.size() - convex_hull(g).size());
  }
  return 0;
}