#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<math.h>

int main() {
	double x[21], y[21], ans = 0;
	int n = 0;
	while (scanf("%lf,%lf", &x[n], &y[n]) != EOF) {
		n++;
	}
	for (int i = 1; i < n; i++) {
		double s = (x[i] - x[0])*(y[i + 1] - y[0]) - (x[i + 1] - x[0])*(y[i] - y[0]);
		if (s < 0)s *= -1;
		ans += s;
	}
	printf("%.8lf", ans/2);
}

