#include<iostream>
#include<vector>
#include<map>
#include<algorithm>
using namespace std;

typedef pair<double, double> P;

int cross(P a, P b, P c) {
  int x0 = b.first - a.first, y0 = b.second - a.second;
  int x1 = c.first - a.first, y1 = c.second - a.second;
  return x0*y1 - x1*y0;
}

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

int main() {
  int n;
  while(cin >> n && n) {
    vector<P> ps, qs;
    for(int i=0; i<n; ++i) {
      double x, y; char dum;
      cin >> x >> dum >> y;
      ps.push_back(P(x, y));
    }
    qs = convex_hull(ps);
    cout << (n - qs.size() + 1) << endl;
  }
  return 0;
}