#include <bits/stdc++.h>

using namespace std;

class Vector {
    public:
        double x, y;

        Vector(double x = 0.0, double y = 0.0) : x(x), y(y) {}

        Vector operator -(Vector v) { return Vector(x - v.x, y - v.y); }

        double abs() { return sqrt(x * x + y * y); }
};

double heron(double a, double b, double c) {
    double s = (a + b + c) / 2;
    return sqrt(s * (s - a) * (s - b) * (s - c));
}

int main() {
    vector<Vector> v(20);
    int n;
    double x, y;
    for (n = 0; scanf("%lf,%lf", &x, &y) != EOF; n++)
        v[n] = Vector(x, y);
    
    double ans = 0;
    for (int i = 1; i + 1 < n; i++) {
        double a = (v[i] - v[0]).abs(),
               b = (v[i + 1] - v[0]).abs(),
               c = (v[i + 1] - v[i]).abs();
        ans += heron(a, b, c);
    }

    printf("%.10f\n", ans);

    return 0;
}
