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

#define X first
#define Y second
typedef pair<double, double> Point;

double sq(double a) {return a*a;}

double gD(Point p1, Point p2) {
  return sqrt( sq(p1.X-p2.X)+sq(p1.Y-p2.Y) );
}

int main() {
  Point p[123456];
  char ch;
  int n=0;
  for(int i=0;cin>>p[i].X>>ch>>p[i].Y;i++) n++;
  double S=0;
  for(int i=1; i<n-1; i++) {
    double a=gD(p[0],p[i]), b=gD(p[i],p[i+1]), c=gD(p[i+1],p[0]);
    double z=(a+b+c)/2;
    S+=sqrt(z*(z-a)*(z-b)*(z-c));
  }
  printf("%.8f\n", S);
  
  return 0;
}