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

#define EPS 1e-15

double dis(P p1, P p2)
{
	double dx = p1.first - p2.first;
	double dy = p1.second - p2.second;
	
	return sqrt(dx * dx + dy * dy);
}

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 = 1; i < polygon.size() - 1; i++){
		double a, b, c;
		
		a = dis(polygon[i], polygon[0]);
		b = dis(polygon[i + 1], polygon[0]);
		c = dis(polygon[i + 1], polygon[i]);
		double z = (a + b + c) / 2;
		s += sqrt(z * (z - a) * (z - b) * (z - c));
	}
	//printf("%.30f\n", s);
	//printf("%.30f\n", EPS);
	//printf("%.30f\n", s + EPS);
	printf("%.7f\n", s);
}