#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)/2.0;
    }
    printf("%.6f\n", abs(sum));
}
