#include <iostream>
#include <complex>
#include <vector>
#include <algorithm>

using namespace std;

const double EPS = 1e-8;
const double INF = 1e12;

typedef complex<double> point;

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

double cross(const point& a, const point& b) {
    return imag(conj(a)*b);
}

double dot(const point& a, const point& b) {
    return real(conj(a)*b);
}

int ccw(point a, point b, point 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;
}

vector<point> convex_hull(vector<point> ps) {
    int n = ps.size(), k = 0;
    sort(ps.begin(), ps.end());
    vector<point> 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;
    char ch;

    while (cin >> n, n) {
        vector<point> input(n);
        vector<point> convex;
        
        for (int i = 0; i < n; i++) 
            cin >> input[i].real() >> ch >> input[i].imag();
        convex = convex_hull(input);
        cout << n - convex.size() << endl;
    }

    return 0;
}