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

int main() {

  double sum = 0;

  string s;
  int x[21],y[21];


  int count = 0;
  while(cin >> s) {
    
    double t = 1;
    double a=0,b=0;
    int flg = 0;
    for(int i=0;i<s.size();i++) {
      if(s[i] == '.'){
	t*=0.1;
	continue;
      }
      if(s[i] == ','){
      t = 1;
      flg = 1;
      continue;
      }
      if(s[i] >= '0' && s[i] <='9'){
	if(flg == 0) a += (s[i]-'0')*t;
	else b += (s[i]-'0')*t;
      }
    if(t < 1) t*=0.1;
    }

    if(s[0] == '-') a+= -1;
    for(int i = 1;i<s.size();i++)
      if(s[i] == '-') {
	b *=-1;
	break;
      }
  

    //  cout << a <<" , " << b << endl;

  x[count] = a;
  y[count] = b;
  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){
	dis[1] = t;
	minx[1]=x[i];
	miny[1]=y[i];
      }
    }
    double hen[3];
    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;
}
  