#include<iostream>
#include<math.h>
#include<stdio.h>

#define FOR(i,j,k) for((i)=(j);(i)<(k);i++)

using namespace std;

int main(void)
{
	int n=0;
	double x[20],y[20];
	double ans=0;
	while(scanf("%lf,%lf",&x[n],&y[n])!=EOF) n++;
	for(int i=1;i<=n-2;i++){
		double a=sqrt((x[0]-x[i])*(x[0]-x[i])+(y[0]-y[i])*(y[0]-y[i]));
		double b=sqrt((x[i]-x[i+1])*(x[i]-x[i+1])+(y[i]-y[i+1])*(y[i]-y[i+1]));
		double c=sqrt((x[i+1]-x[0])*(x[i+1]-x[0])+(y[i+1]-y[0])*(y[i+1]-y[0]));
		double z=(a+b+c)/2;
		double s=sqrt(z*(z-a)*(z-b)*(z-c));
		ans+=s;
	}
	cout<<ans<<endl;
}