#include<iostream>
#include<cstdio>
#include<complex>
#include<cmath>
using namespace std;
typedef complex<double> xy_t;
int main()
{
  xy_t P[110];
  int N = 0;
  double x,y;
  while(~scanf("%lf,%lf",&x,&y)){
    P[N++] = xy_t(x,y);
  }
  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]; 
      sum += (conj(b - a) * (c - a)).imag();
  }
  sum /= 2;
  printf("%.6f\n",abs(sum));
  return 0;
}