#include <iostream>
#include <string>
#include <cmath>
#include <cstdio>
using namespace std;

int main() {

  double sum = 0;

  double  x[21],y[21];

  int count = 0;
  while(scanf("%lf,%lf",&x[count],&y[count]) != EOF) {
  
  count ++;
  if(count >= 3) {
    double z;
    int minx[2],miny[2];
    double dis[2] = {10000000,100000000};
    double t;
    int mae;
    for(int i=0;i<count-1;i++) {
      t = sqrt(((x[count-1]-x[i])*(x[count-1]-x[i]) + (y[count-1]-y[i])*(y[count-1]-y[i])));
      if(dis[0] > t){
	//cout << t << endl;
	dis[0] = t;
	minx[0]=x[i];
	miny[0]=y[i];
	mae = i;
      }
    }
    for(int i=0;i<count-1;i++) {
      t =  sqrt(((x[count-1]-x[i])*(x[count-1]-x[i]) + (y[count-1]-y[i])*(y[count-1]-y[i])));
      if(dis[1] > t && mae != i){
	if( (x[count-1] == minx[0] && x[count-1] == x[i] && x[i] == minx[0])  ||  (y[count-1] == miny[0] && miny[0] == y[i] && y[count-1] == y[i]) ) continue;
	//	cout << "ok" << endl;
	dis[1] = t;
	minx[1]=x[i];
	miny[1]=y[i];
      }
    }
    if(dis[1] == 100000000) continue;
    double hen[3];
    //    cout << dis[0] <<" " << dis[1] << endl;
    hen[0] =  sqrt((x[count-1]-minx[0])*(x[count-1]-minx[0]) + (y[count-1]-miny[0])*(y[count-1]-miny[0]));
    hen[1] =  sqrt((x[count-1]-minx[1])*(x[count-1]-minx[1]) + (y[count-1]-miny[1])*(y[count-1]-miny[1]));
    hen[2] =  sqrt((minx[0]-minx[1])*(minx[0]-minx[1]) + (miny[0]-miny[1])*(miny[0]-miny[1]));
    z = (hen[0] + hen[1] + hen[2]) /2;
    sum += sqrt(z*(z-hen[0])*(z-hen[1])*(z-hen[2]));
  }
    
    }
  
  printf("%l.8f\n",sum);

  return 0;
}
  