#include<stdio.h> 

int main() { 
 double x[22], y[22], ans = 0; 
 int n = 0; 
 while (~scanf("%lf,%lf", &x[n], &y[n])) { 
  n++; 
 } 
 double s; 
 for (int i = 1; i < n; i++) { 
  s = (x[i] - x[0])*(y[i + 1] - y[0]) - (x[i + 1] - x[0])*(y[i] - y[0]); 
  if (s < 0)s = -s; 
  ans += s; 
 } 
 printf("%.8lf", ans/2.0); 
}
