#include <complex>
#include <cmath>
#include <stdio.h>
typedef complex<double> xy_t;
using namespace std;

xy_t P[110];

int main(){
	int N = 0;
	double x, y;
	while (~scanf("%lf,%lf", &x, &y)) {
		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 += (conj(b-a)*(c-a)).imag())/2;
	}
	printf("%.6f\n",abs(sum));
}