// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0079
// Title : Area of Polygon
/*

?????????????????¨???????§£????????¨??????????????£????????????????????????
????????????????????\??????????´???°??¨??????????????±??????1????????????p[0]?????????????????????????????£?????????2??????????????????????????????????§???¢????¬????????????¢???????????????????±?????????????????????????????????????????????????????????¶???????????¨??£????????????????????????????????????
*/
#include <iostream>

#include <complex>
#include <cmath>
#include <cstdio>

using namespace std;
int main() {
	typedef complex<double> xy;
	xy p[20];
	int n = 0;
	double x, y, s;
	while ( ~scanf( "%lf, %lf", &x, &y ) ) {

		p[n++] = xy( x, y );
	}

	for ( int i = 1; i < n - 1; i++ ) {
		s += ( conj( p[i] - p[0] ) * ( p[i + 1] - p[0] ) ).imag() / 2;
	}

	printf( "%.6f\n", abs(s) );
}