#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstdio>
#include<vector>
using namespace std;

int main(){
    vector<int> x, y;
    double a, b, c, s;
    while(~scanf("%lf,%lf", &a, &b)){
	x.push_back(a);
	y.push_back(b);
    }
    double res = 0;
    for(int i = 1;i < x.size() - 1;i++){
	a = hypot(x[0] - x[i], y[0] - y[i]);
	b = hypot(x[0] - x[i + 1], y[0] - y[i + 1]);
	c = hypot(x[i] - x[i + 1], y[i] - y[i + 1]);
	s = (a + b + c) / 2;
	res += sqrt(s * (s - a) * (s - b) * (s - c));
    }
    printf("%.9lf\n", res);
    return 0;
}