#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <cmath>
#include <memory.h>
#include <cassert>

using namespace std;


#define all(c) ((c).begin()), ((c).end())
#define debug(c) cerr << "> " << #c << " = " << (c) << endl;
#define iter(c) __typeof((c).begin())
#define present(c, e) ((c).find((e)) != (c).end())
#define cpresent(c, e) (find(all(c), (e)) != (c).end())
#define tr(i, c) for (iter(c) i = (c).begin(); i != (c).end(); i++)
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, a, b) for (int i = (int)(a); i <= (int)(b); i++)

#define mp make_pair
#define fst first
#define snd second
#define pb push_back


const double EPS = 1e-10;


typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef complex<double> P;


inline double det(const P &a, const P &b) {
	return (conj(a) * b).imag();
}

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


vector<P> convexHull(vector<P> ps) {
	int n = ps.size(), k = 0;
	
	if (n <= 1) return ps;
	
	sort(all(ps));
	vector<P> qs(n * 2);
	for (int i = 0; i < n; qs[k++] = ps[i++]) {
		while (k > 1 && det(qs[k - 1] - qs[k - 2], ps[i] - qs[k - 1]) < EPS) k--;
	}
	for (int i = n - 2, t = k; i >= 0; qs[k++] = ps[i--]) {
		while (k > t && det(qs[k - 1] - qs[k - 2], ps[i] - qs[k - 1]) < EPS) k--;
	}
	
	vector<P> res(qs.begin(), qs.begin() + k - 1);
	return res;
}

int main() {
	for (int n; cin >> n, n != 0; ) {
		vector<P> ps;
		rep(i, n) {
			char c;
			double x, y; cin >> x >> c >> y;
			ps.pb(P(x, y));
		}
		cout << n - convexHull(ps).size() << endl;
	}
	return 0;
}