#include <cstdio>
#include <cmath>
#include <utility>
#include <vector>
#include <algorithm>
using namespace std;
typedef pair<double, double> P;

int main()
{
	vector<P> polygon;
	P tmp;
	
	while (scanf("%lf,%lf", &tmp.first, &tmp.second) != EOF){
		polygon.push_back(tmp);
	}
	sort(polygon.begin(), polygon.end());
	double s = 0;
	
	for (int i = 0; i < polygon.size() - 2; i++){
		double len[3];
		
		for (int j = 0; j < 3; j++){
			double dx = polygon[i + (j + 1) % 3].first - polygon[i + j].first;
			double dy = polygon[i + (j + 1) % 3].second - polygon[i + j].second;
			len[j] = sqrt(dx * dx + dy * dy);
		}
		double z = (len[0] + len[1] + len[2]) / 2;
		double ms = sqrt(z * (z - len[0]) * (z - len[1]) * (z - len[2]));
		s += ms;
	}
	printf("%.10f\n", s);
}