#include <cstdio>
#include <cmath>
#include <algorithm>
using namespace std;

typedef struct
{
	double x;
	double y;
} POINT;

POINT v[100];

bool cmp(POINT A, POINT B)
{
	if (A.x == B.x){
		return (A.y < B.y);
	}
	return (A.x < B.x);
}

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

int main()
{
	int m = 0;
	
	while (scanf("%lf,%lf", &v[m].x, &v[m].y) != EOF){
		m++;
	}
	
	sort(v, v + m, cmp);

/*	
	for (int i = 0; i < m; i++){
		printf("%lf %lf\n", v[i].x, v[i].y);
	}
*/
	
	double S = 0.0;
	
	for (int i = 0; i < m - 1; i++){
		double a = dif(v[0].y - v[i].y, v[0].x - v[i].x);
		double b = dif(v[i].y - v[i + 1].y, v[i].x - v[i + 1].x);
		double c = dif(v[i + 1].y - v[0].y, v[i + 1].x - v[0].x);
		double z = (a + b + c) / 2;
		
//		printf("%lf %lf %lf %lf\n", a, b, c, z);
		
		S += sqrt(z * (z - a) * (z - b) * (z - c));
		
//		printf("%lf\n", S);
	}
	
	printf("%lf\n", S);
	
	return 0;
}