#include <iostream>
#include <stdio.h>
#include <cmath>

double area_of_polygon(double ax, double ay, double bx, double by, double cx, double cy);
double distance(double ax, double ay, double bx, double by);

using namespace std;
int main(){
  double firstx, firsty, ax, ay, bx, by;
  scanf("%lf,%lf", &firstx, &firsty);
  scanf("%lf,%lf", &ax, &ay);
  scanf("%lf,%lf", &bx, &by);

  double area = 0;
  area += area_of_polygon(firstx, firsty, ax, ay, bx, by);
  bx = ax;
  by = ay;

  while(scanf("%lf,%lf", &ax, &ay)!=EOF){
    area += area_of_polygon(firstx, firsty, ax, ay, bx, by);
    bx = ax;
    by = ay;
  }
  cout << area << endl;
}

double area_of_polygon(double ax, double ay, double bx, double by, double cx, double cy){
  double disa = distance(ax, ay, bx, by);
  double disb = distance(cx, cy, bx, by);
  double disc = distance(ax, ay, cx, cy);
  double z = (disa+disb+disc)/(double)2;
  return sqrt(z*(z-disa)*(z-disb)*(z-disc));
}

double distance(double ax, double ay, double bx, double by){
  return sqrt((ax-bx)*(ax-bx) + (ay-by)*(ay-by));
}