#include <complex>
#include <cmath>

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);
  }
  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 += ((b.real()-a.real())*(c.imag()-a.imag())+(c.real()-a.real())*(b.imag()-a.imag()))/2.0;
  }
  printf("%.6f",abs(sum));
}