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

int main(){
    double x[20], y[20], area = 0;
    int i = 0;
    while( scanf("%lf,%lf", &x[i], &y[i]) != EOF) i++;
    for(int j = 1; j < i; j++){
        area += (x[j-1]*y[j] - x[j]*y[j-1])/2;
    }
    printf("%lf\n", abs(area));
    return 0;
}