#include<cstdio>
#include<cmath>
#include<complex>
#include<string>
#include<map>
using namespace std;
typedef complex<double> xy_t;
xy_t P[110];

int main(){
  int N=0;
  double x,y;
  while(~scanf("%lf,%lf",&x,&y)){
      P[N]=xy_t(x,y);
      N++;
      }
  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(c-a)*(b-a)).imag())/2.0;
  }

  printf("%.6f\n",abs(sum));
  return 0;

}