#include <iostream>
#include <complex>
#include <cmath>
#include <cstdio>
using namespace std;
typedef complex<double> xy_t;

double dot_product(xy_t a, xy_t b) { return (conj(a) * b).real(); }
double cross_product(xy_t a, xy_t b) { return (conj(a) * b).imag(); }
xy_t projection(xy_t p, xy_t b) { return b * dot_product(p, b) / norm(b); }

int main()
{
    int n=0;
    double x, y;
    xy_t P[110];
    while (~scanf("%lf,%lf", &x, &y))
    {
        P[n++] = xy_t(x, y);
    }
    double sum = 0.0;
    for (int i = 0; i + 2 < n; i++)
    {
        sum += cross_product(P[i + 1] - P[0], P[i + 2] - P[0]) / 2;
    }
    cout << abs(sum) << endl;
    return 0;
}

