#include<iostream>
#include<complex>
#include<cmath>
#include<vector>
using namespace std;

typedef complex<double> xy_t;
vector <xy_t> v;

double heron(xy_t p1, xy_t p2, xy_t p3) {
    double a = abs(p2 - p1);
    double b = abs(p3 - p2);
    double c = abs(p1 - p3);
    double s = (a + b + c) / 2;
    return sqrt(s*(s - a)*(s - b)*(s - c));
}
int main()
{
    double x, y;
    char c;
    while (cin >> x >> c >> y) {
        complex<double> tmp(x, y);
        v.push_back(tmp);
    }
    double sum = 0;
    for (int i = 1; i < v.size() - 1; i++) {
        sum += heron(v[0], v[i], v[i + 1]);
    }
    cout << sum << endl;
    return 0;
}