#include <iostream>
#include <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;


double cross_product(xy_t a, xy_t b);
xy_t P[110];

int main() {
	double x1,y1,x2,y2;
	double xin,yin;
	char c;
	double sum = 0;
	int N = 0;

	scanf("%lf,%lf",&xin,&yin);
	xy_t C(1,2);
	xy_t D(3,4);
	//cout << cross_product(C,D) << endl;
	while(scanf("%lf,%lf",&x1,&y1)+1) {
		//cout << x1 << " " <<  y1 << endl;
		if(N == 0) { 
			x2 = x1; y2 = y1; scanf("%lf,%lf",&x1,&y1);
			N++;
			//cout << x1 << " " <<  y1 << endl;
		}
		if(x1 == x2 && y1 == y2 && N > 2) break;
		xy_t A(x1-xin,y1-yin);
		xy_t B(x2-xin,y2-yin);
		//cout << cross_product(A,B) << endl;
		sum += cross_product(A,B)/2;
		x2 = x1; y2 = y1;
		N++;
	}
	cout << sum << endl;
}

double cross_product(xy_t a, xy_t b) {
	return (conj(a)*b).imag();
}