#include <iostream>
#include <cmath>
#include <vector>
#include <algorithm>

using namespace std;

double EPS = 1e-10;

double add (double a, double b) {
	if (abs(a + b) < EPS * (abs(a) + abs(b))) {
		return 0;
	}
	return a + b;
}

struct P {
	double x, y;
	P() {}
	P (double x, double y) : x(x), y(y) {
	}
	P operator + (P p) {
		return P(add(x, p.x), add(y, p.y));
	}
	P operator - (P p) {
		return P(add(x, -p.x), add(y, -p.y));
	}
	P operator * (double d) {
		return P(x * d, y * d);
	}
	double dot(P p) {
		return add(x * p.x, y * p.y);
	}
	double det(P p) {
		return add(x * p.y, -y * p.x);
	}
};

bool cmp_x(const P& p, const P& q) {
	if(p.x != q.x) {
		return p.x < q.x;
	}
	return p.y < q.y;
}

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

int main() {
	int n;
	while (cin >> n) {
		if (n == 0) {
			break;
		}
		char c;
		P ps[110];
		for (int i = 0; i < n; i++) {
			cin >> ps[i].x >> c >> ps[i].y;
		}
		vector<P> qs = convex_hell(ps, n);
		cout << n - qs.size() << endl;
	}
	return 0;
}