#include <cstdio>
#include <vector>
#include <iomanip>
#include <cmath>
using namespace std;

const double PI = 3.1415926535;

double angle(double cur, double next){
    double r = cur - next + 2*PI;
    while( r >= 2*PI ) r -= 2*PI;
    return r;
}

int main(){
    int n;
    double x[100], y[100];
    while( scanf("%d", &n), n ){
        double cx = 10000, cy = 10000;
        int mem = 0;
        for(int i = 0; i < n; i++){
            scanf("%lf,%lf", x+i, y+i);
            if( x[i] < cx ){
                cx = x[i]; cy = y[i];
                mem = i;
            }
        }
        vector<bool> used(100, false);
        used[mem] = true;
        double cang = atan2(1, 0);
        double lv;
        int ln = mem;
        int i;
        for(i = 0; i < n; i++){
            lv = 100;
            int can = ln;
            for(int j = 0; j < n; j++){
                if( ln == j ) continue;
                double ang = angle( cang,
                                    atan2(y[j]-cy, x[j]-cx) );
                if( ang < lv ){
                    lv = ang; can = j;
                }
            }
            ln = can;
            cang = atan2(y[ln]-cy, x[ln]-cx);
            cx = x[ln]; cy = y[ln];
            if( used[ln] ) break;
            used[ln] = true;
        }
        printf("%d\n", n-i-1);
    }
    return 0;
}