#include "bits/stdc++.h"
using namespace std;
typedef complex<double> xy_t;
double cross_product(xy_t a, xy_t b) { return (conj(a) * b).imag(); }

xy_t P[110];
int main() {
	int N=0;
	double x, y;
	while (scanf("%lf,%lf", &x, &y) != EOF) { //入力ループは"\n"で抜ける
		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;
	}
	printf("%.6f\n", abs(sum));
}

