#include <iostream>
#include <complex>
#include <cmath>
#include <cstdio>
using namespace std;

int main() {
	typedef complex<double> xy;
	double x1, y1, x2, y2, s;
	xy z1, z2;
	s = 0.0;
	scanf( "%lf, %lf", &x1, &y1 );
	while ( ~scanf( "%lf, %lf", &x2, &y2 ) ) {
		z1 = xy( x1, y1 );
		z2 = xy( x2, y2 );
		s += ( conj( z1 ) * z2 ).real() / 2;
		x1 = x2;
		y1 = y2;
	}
	printf( "%.6f?\n", abs(s) );
}