#include <iostream>
#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) != EOF)
        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)/2;
    }
    printf("%.6f\n",abs(sum));
    return 0;
}
