#include <iostream>
#include <stdio.h>
#include <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;
// ??????: a.x*b.x
double dot_product(xy_t a, xy_t b) { 
  return (conj(a)*b).real(); 
}
// ??????: a.x*b.y - b.x*a.y
// ????§???¢????¬????????????¢????????????
double cross_product(xy_t a, xy_t b) { 
  return (conj(a)*b).imag(); 
}
// ?????±: ????????¨ p ??????????????´?????? b ????????±
xy_t projection(xy_t p, xy_t b) { 
  return b*dot_product(p,b)/norm(b); 
}
xy_t P[110];
int main() {
  int N=0;
  double x, y;
  while (scanf("%lf,%lf", &x, &y) != EOF) {
    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];
    // ????§???¢ abc ?????¢??????????¨?
    sum += fabs(cross_product(c-a,c-b))/2;
  }
  printf("%.6f\n", abs(sum));
}