#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

double length(double xa,double ya, double xb, double yb)
{
	return sqrt((xa-xb)*(xa-xb)+(ya-yb)*(ya-yb));
}

double hellon(double ra, double rb, double rc)
{
	double z = (ra+rb+rc)/2;
	return sqrt(z*(z-ra)*(z-rb)*(z-rc));
}

int main()
{
	double xa,xb,xc,ya,yb,yc;
	char dot;
	cin >> xa >> dot >> ya;
	cin >> xb >> dot >> yb;
	cin >> xc >> dot >> yc;
	double S = hellon(length(xa,ya,xb,yb),length(xb,yb,xc,yc),length(xc,yc,xa,ya));
	xb = xc; yb = yc;
	while(cin >> xc >> dot >> yc){
		S += hellon(length(xa,ya,xb,yb),length(xb,yb,xc,yc),length(xc,yc,xa,ya));
	}
	cout << setprecision(6) << fixed << S << endl;
	return 0;
}