#include<stdio.h>
#include<cmath>
#include<complex>
using namespace std;
#if 0
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#endif

typedef complex<double> xy_t;
xy_t P[20];
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[i+1]-P[0],b=P[i+2]-P[0];
        sum+=cross_product(a,b)/2.0;
    }

        printf("%.6f\n",abs(sum));

}