#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
class Point {
public:
	long double px, py;
	Point() : px(0), py(0) {};
	Point(long double px_, long double py_) : px(px_), py(py_) {};
	bool operator==(const Point& p) const { return px == p.px && py == p.py; }
	bool operator!=(const Point& p) const { return px != p.px || py != p.py; }
	bool operator<(const Point& p) const { return px < p.px ? true : (px == p.px && py < p.py); }
	Point operator-(const Point& p) const { return Point(px - p.px, py - p.py); }
};
long double norm(const Point& a) { return a.px * a.px + a.py * a.py; }
long double dot(const Point& a, const Point& b) { return a.px * b.px + a.py * b.py; }
long double crs(const Point& a, const Point& b) { return a.px * b.py - a.py * b.px; }
int ccw(const Point& p0, const Point& p1, const Point& p2) {
	Point a = p1 - p0, b = p2 - p0;
	if (crs(a, b) > 1e-10) return 1;
	if (crs(a, b) < -1e-10) return -1;
	if (dot(a, b) < -1e-10) return 2;
	if (norm(a) < norm(b)) return -2;
	return 0;
}
vector<Point> convex_hull(vector<Point> v) {
	if (v.size() < 3) return v;
	sort(v.begin(), v.end());
	vector<Point> u = { v[0], v[1] }, l = { v[v.size() - 1], v[v.size() - 2] };
	for (int i = 2; i < v.size(); i++) {
		for (int n = u.size(); n >= 2 && ccw(u[n - 2], u[n - 1], v[i]) >= 0; n--) u.pop_back();
		u.push_back(v[i]);
	}
	for (int i = v.size() - 3; i >= 0; i--) {
		for (int n = l.size(); n >= 2 && ccw(l[n - 2], l[n - 1], v[i]) >= 0; n--) l.pop_back();
		l.push_back(v[i]);
	}
	reverse(l.begin(), l.end());
	for (int i = u.size() - 2; i >= 1; i--) l.push_back(u[i]);
	return l;
}
int main() {
	vector<Point>vec; Point p; char c;
	while (true) {
		int n; cin >> n;
		vec.clear();
		if (n == 0) { break; }
		for (int i = 0; i < n; i++) {
			cin >> p.px >> c >> p.py;
			vec.push_back(p);
		}
		cout << n - convex_hull(vec).size() << endl;
	}
}