#include <complex>
#include <cmath>
#include <iostream>
using namespace std;

typedef complex<double> xy_t;
xy_t P[110];

int main() {
  //入力例　読み込んだ点の個数をNとする
  int N = 0;
  double x,y;
  while (~scanf("%lf,%lf", &x, &y)) {
    P[N++] = xy_t(x,y);
	}
	//面積計算
	double sum = 0.0;
	for (int i = 0; i+2 < N; ++i) {
	  xy_t a = P[0], b = P[i+1], c = P[i+2];
	  xy_t ab = P[i+1] - P[0], bc = P[i+2] - P[i+1], ca = P[0] - P[i+2];
	  double z = (abs(ab) + abs(bc) + abs(ca))/2;
	  double s = sqrt(z*(z-abs(ab))*(z-abs(bc))*(z-abs(ca)));
	  sum += s;
	  }
	printf("%.6f\n", abs(sum));
}