/*
	0079:Area of Polygon
*/
#include	<iostream>
#include	<vector>
#include	<utility>
#include	<cstdio>

using namespace std;

typedef pair<double, double> P_DD;

int main(void) {
	double x, y, sx, sy, sum = 0.0;
	vector<P_DD> data;
	bool fir = true;
	
	while( scanf("%lf,%lf", &x, &y) != EOF) {
		if(fir) {
			sx = x;	sy = y;
			fir = false;
		}
		data.push_back( P_DD(x, y) );
	}
	data.push_back( P_DD(sx, sy) );
	
	vector<P_DD>::iterator it = data.begin();
	
	while( it+1 != data.end() ) {
		double b1x = (*it).first, b1y = (*it).second, b2x = (*(it+1)).first, b2y = (*(it+1)).second;
		
		sum += (b1x - b2x) * (b1y + b2y);
		it++;
	}
	sum /= 2;
	if(sum < 0) { sum *= -1.0; }
	printf("%f\n", sum);
	
	return 0;
}