#include<iostream>
#include<cstdio>
#include<complex>
#include<cmath>

using namespace std;

typedef complex<double> xy_t;
double cross(xy_t a,xy_t b);
xy_t P[20];



int main(){

  int N;

  double x,y;
  int i=0;
  while(scanf("%lf,%lf",&x,&y) != EOF){
    P[i] = xy_t(x,y);
    i++;
    
  }
  N=i;
  double ans=0;
  for(int j=1;j<N;j++){
    ans+=cross(P[j]-P[0],P[j+1]-P[0]);
  }

  ans=abs(ans)/2;

  printf("%lf\n",ans);
  
}
double cross(xy_t a, xy_t b){return (conj(a)*b).imag();}