#include <iostream>
#include <vector>
#include <algorithm>
#include <math.h>
using namespace std;
typedef long long int ll;

double s(double z,double a,double b,double c){
	return sqrt(z*(z-a)*(z-b)*(z-c));
}

double dist(double a,double b,double c,double d){
	return sqrt((a-c)*(a-c)+(b-d)*(b-d));
}

int main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	vector<double> x,y;
	double p,q;
	char cc;
	while(cin >> p >> cc >> q){
		x.push_back(p);
		y.push_back(q);
	}
	int n=x.size();
	double ans=0.0;
	for(int i=1;i<n-1;i++){
		double a=dist(x[i],y[i],x[i+1],y[i+1]);
		double b=dist(x[i+1],y[i+1],x[0],y[0]);
		double c=dist(x[i],y[i],x[0],y[0]);
		double z=(a+b+c)/2.0;
		ans+=s(z,a,b,c);
	}
	printf("%.8f\n",ans);
}
