#include<stdio.h>
int main() {
	double x[22], y[22], ans = 0;
	int n = 0;
	while (~scanf("%lf,%lf", &x[n], &y[n])) {
		n++;
	}
	double s;
	for (int i = 1; i < n; i++) {
		s = (x[i] - x[0])*(y[(i + 1)%n] - y[0]) - (x[(i + 1)%n] - x[0])*(y[i] - y[0]);
		if (s < 0)s = -s;
		ans += s;
	}
	printf("%.8lf", ans/2.0);
}
