#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<utility>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<complex>

using namespace std;
typedef pair<int,int> PII;
typedef long long ll;
typedef complex<double> P;

#define EQ(a,b) (abs((a)-(b)) < EPS)
#define EQV(a,b) ( EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()) )
const double EPS = 1e-10;

namespace std{
	bool operator < (const P& a, const P& b) {
		return EQ(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);
	}
}

//ツ点ツづ個進ツ行ツ陛サツ古シ
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;
}

//ツ禿環陛ッ
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++]) // lower-hull
    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--]) // upper-hull
    while (k >= t && ccw(ch[k-2], ch[k-1], ps[i]) <= 0) --k;
  ch.resize(k-1);
  return ch;
}

int main(){
  int n;
	double a,b;
	vector<P> points;
	while(true){
		cin>>n;
		if(!n)break;
		points.clear();
		for(int i=0;i<n;i++){
			scanf("%lf,%lf",&a,&b);
			points.push_back(P(a,b));
		}

		vector<P> hull = convex_hull(points);
		cout<<n-hull.size()<<endl;
	}
	
  return 0;
}