#include<bits/stdc++.h>

using namespace std;

const double EPS = 1e-8;
const double INF = 1e12;
typedef complex<double> P;



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

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

struct L : public vector<P> {
    L(const P &a, const P &b) {
        push_back(a); push_back(b);
    }
};

typedef vector<P> G;

struct C {
    P p; double r;
    C(const P &p, double r) : p(p), r(r) { }
};

vector<P> convex_hull(vector<P> ps) {
    int n = ps.size(), k = 0;
    sort(ps.begin(), ps.end());
    vector<P> 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;
    while(cin >> n, n){
        vector<P> v;
        for(int i=0; i< n; i++){
            double x, y;
            scanf("%lf,%lf", &x, &y);
            P p;
            p.real(x); p.imag(y);
            v.push_back(p);
        }
        vector<P> q =  convex_hull(v);
        cout << n-q.size() << endl;
    }
}