
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <ctime>
#include <string>
#include <map>
#include <stack>
#include <queue>
#include <complex>

using namespace std;

typedef complex<double> xy_t;
char c;
xy_t P[20];
const int MAX = 10000000;

int main(void){

	for (int i = 0; i < 20; ++i){
		P[i] = xy_t(MAX, MAX);
	}

	for (int i = 0; i < 20; ++i){
		double x, y;
		cin >> x >> c >> y;
		P[i] = xy_t(x, y);
	}
	double ans = 0;

	for(int i = 1; i < 20; i++){
		if(P[i + 1].real() != MAX){
			ans += cross_product(xy_t (P[i] - P[0]), xy_t (P[i + 1] - P[0]))
		}
	}

	cout << ans << endl;
	
    return 0;
}