#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <string>
#include <map>
#include <queue>
#include <stack>
#include <cstring>
#include <cmath>
#include <deque>
#include <set>
#include <complex>

#define P_P    const P& a, const P& b

using namespace std;

typedef long long int lint;
typedef complex<double> P;

namespace std {
bool operator < (P_P){
    return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
}
}
double cross(P_P){ return imag(conj(a) * b); }
double dot(P_P){ return real(conj(a) * b); }
int ccw(P a, P b, P c){
    b -= a; c -= a;
    if (cross(b, c) > 0)   return +1;
    if (cross(b, c) < 0)   return -1;
    if (dot(b, c) < 0)     return +2;
    if (norm(b) < norm(c)) return -2;
    return 0;
}
typedef vector<P> G;

G convex_hull(G ps){
    int n = ps.size(), k = 0;
    sort(ps.begin(), ps.end());
    G ch(2 * n);
    for (int i = 0; i < n; ch[k++] = ps[i++]){
        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--]){
        while (k >= t && ccw(ch[k - 2], ch[k - 1], ps[i]) <= 0) --k;
    }
    ch.resize(k - 1);
    return ch;
}

template<typename T> inline bool in(T& x){ return cin >> x; }
template<typename T> inline T in(){T x; cin >> x; return x; }

int main()
{
    int n;

    while (scanf("%d", &n), n){
        G g;
        for (int i = 0; i < n; i++){
            double x, y;
            scanf("%lf,%lf", &x, &y);
            g.push_back(P(x, y));
        }
        printf("%zu\n", g.size() - convex_hull(g).size());
    }
	return (0);
}