#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<stack>
#include<queue>
#include<set>
#include<map>
#include<vector>
#include<list>
#include<algorithm>
#include<utility>
#include<complex>

using namespace std;

#define input_init stringstream ss; string strtoken, token; istringstream is
#define input_line  getline(cin, strtoken);is.str(strtoken);is.clear(istringstream::goodbit)
#define input_token(num) ss.str(""); ss.clear(stringstream::goodbit); getline(is, token, ','); ss << token; ss >> num


namespace geo{
#include<vector>
#include<algorithm>
#include<complex>	

	typedef complex<double> P;
	typedef vector<P> Poly;
	const double eps = 1e-8;

	//?????????????????????????????????????????¨???
	inline void x(P& p, double n){ p.real(n); }
	inline void y(P& p, double n){ p.imag(n); }
	inline double x(P& p){ p.real(); }
	inline double y(P& p){ p.imag(); }

	//????????????a??¨b?????????
	inline double dot(const P a, const  P b){//A dot B
		return a.real()*b.real() + a.imag()*b.imag();
	}

	//????????????a??¨b?????????
	inline double cross(const P a, const P b){//A cross B
		return a.real()*b.imag() - a.imag()*b.real();
	}


	// ?????????????????¨??????????????????????????????????????????
	int comp(const P &l, const P &r){
		if (l.real() == r.real())
			return(l.imag() < r.imag());
		return(l.real() < r.real());
	}

	// ??????p??????????????????????¨?????????§Poly???????´?
	// Poly p : ?????¨????????????
	// ???????????§O(nlogn)
	inline Poly convex_hull(Poly& p){
		int n = (int)p.size();
		Poly res(2 * n);
		int k = 0, t;
		sort(p.begin(), p.end(),comp);
		for (int i = 0; i < n; i++){
			while (k > 1 && (cross(res[k - 1] - res[k - 2], p[i] - res[k - 1]) < eps))k--;
			res[k++] = p[i];
		}
		t = k;
		for (int i = n - 2; i >= 0; i--){
			while (k > t && (cross(res[k - 1] - res[k - 2], p[i] - res[k - 1]) < eps))k--;
			res[k++] = p[i];
		}
		res.resize(k - 1);
		return res;
	}


	// ???p?????????????????¨????????¨????????????true
	// Poly l : ???????¨????????????????,????????°n
	// P p    : ???????????????????????????
	// ?????¨??§????????¢?´¢ O(log n)
	inline bool convex_in(const Poly& l, const P& p){
		int a = 0, b = (int)l.size(), c;
		double A, C;
		const P g = (l[a] + l[b - 1] + l[b / 2]) / 3.0;
		while (b - a > 1){
			c = (a + b) / 2;
			A = cross(l[a] - g, p - l[a]);
			C = cross(l[c] - g, p - l[c]);
			if (cross(l[a] - g, l[c] - g) >= 0){
				if (A > -eps&&C < -eps)b = c;
				else a = c;
			}
			else {

				if (C < -eps || A > -eps)b = c;
				else a = c;
			}
		}
		return(cross(l[b%l.size()] - l[a], p - l[b%l.size()]) > -eps);
	}


	// ??????l?????¢????????????
	// Poly l : ???????¨????????????????,????????°n
	// O(n)
	inline double convex_area(const Poly& l){
		double res = 0;
		int n = (int)l.size();
		for (int i = 2; i < n; i++)
			res += abs(cross(l[1] - l[0], l[i] - l[1]));
		return res;
	}

}

int main(void){
	int n;
	double x, y;
	geo::Poly p;
	input_init;
	while (true){
		input_line;
		input_token(n);
		if (n == 0)break;
		p.resize(n);
		for (int i = 0; i < n; i++){
			input_line;
			input_token(x);
			input_token(y);
			p[i].real(x);
			p[i].imag(y);
		}
		auto q=geo::convex_hull(p);
		cout << n - q.size() << endl;
	}

	return(0);
}