#include <cstdio>
#include <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;
xy_t P[110];

double cross_product(xy_t a, xy_t b) { return (conj(a)*b).imag(); }

int main() {
    int N = 0;
    double x, y;
    while(~scanf("%lf,%lf", &x, &y)) {
        P[N++] = xy_t(x,y);
    }

    double sum = 0.0;
    for(int i = 0; i+2 < N; i++) {
        xy_t a=P[0], b=P[i+1], c=P[i+2];
        sum += cross_product(b-a,c-a)/(double)2;
    }
    printf("%.6f\n", abs(sum));
    
    return 0;
}
