#include<cstdio>
#include<cmath>

struct Point{ double x, y;};

double getDistance(Point p1, Point p2){
    return sqrt( (p1.x-p2.x)*(p1.x-p2.x) + (p1.y-p2.y)*(p1.y-p2.y));
}
main(){
    Point P[20];
    int n = 0;
    double z, S = 0;
    while( scanf("%lf,%lf", &P[n].x, &P[n].y) != EOF ){
	n++;
    }
    for ( int i = 1; i < n-1; i++ ){
	double a = getDistance(P[0], P[i]);
	double b = getDistance(P[i], P[i+1]);
	double c = getDistance(P[0], P[i+1]);
	z = (a + b + c )/2.0;
	S += sqrt(z*(z-a)*(z-b)*(z-c));
    }
    printf("%.8lf\n", S);
}