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

typedef complex<double> P;

class Triangle{

private:
	//Op`ÌR_ÌÀW
	P a, b, c;
	//Op`ÌRÓÌ·³
	double A, B, C;
	//Op`ÌÊÏ
	double s;

public:
	//RXgN^(RÂÌ_ÆÓÆpxðú»)
	Triangle(P p1, P p2, P p3){
		a = p1;
		b = p2;
		c = p3;
		B = abs( c-a );
		A = abs( b-c );
		C = abs( a-b );
		double z = ( A + B + C ) / 2.0;
		s = sqrt( z * (z-A)*(z-B)*(z-C));
	}
	double getArea(){//Op`ÌÊÏðÔ·
		return s;
	}
};

int main(){
	double x,y;
	vector<P> polygon;

	while( scanf("%lf,%lf" , &x , &y ) != EOF ){
		P p(x,y);
		polygon.push_back(p);
	}
	double sum = 0;
	for(int i=1 ; i+1<polygon.size() ; ++i){
		P a = polygon[0];
		P b = polygon[i];
		P c = polygon[i+1];
		Triangle tri(a,b,c);
		
		sum += tri.getArea();
	}
	printf("%.6lf\n" , sum);
}