#include <iostream>
#include <stdio.h>
#include <vector>
#include <algorithm>
#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)!=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];
    sum += ((conj(b-a)*(c-a)).imag())/2.0;
  }
    printf("%.6f\n",abs(sum));
}


  return 0;
}