Problem: Write a program that reads the coordinates of the vertices of a convex n-sided polygon (a polygon whose internal angles are less than 180 degrees, that is, a polygon that is not dented) and outputs its area. The vertices are named Vertex 1, Vertex 2, Vertex 3, ... Vertex n according to the order of edge connections.

However, n is 3 or more and 20 or less. You can also use the following formula to find the area S from the lengths a, b, and c of the three sides of the triangle.

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input

The input is given in the following format:


x1, y1
x2, y2
::
xn, yn


xi and yi are real numbers that represent the x and y coordinates of vertex i, respectively.

output

Outputs the area S (real number) on one line. The output can contain an error of 0.000001 or less.

Example

Input

0.0,0.0
0.0,1.0
1.0,1.0
2.0,0.0
1.0,-1.0


Output

2.500000

Solution (in CPP):

Solution:
#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;

int main()
{
  double x[3],y[3],tx,ty,ans=0;
  int count=0;
  for(;~scanf("%lf,%lf",&tx,&ty);)
    {
      //      cout<<"line "<<count<<endl;
      if(count<3)
	{
	  x[count]=tx;
	  y[count]=ty;
	}
      else
	{
	  x[1]=x[2];
	  y[1]=y[2];
	  x[2]=tx;
	  y[2]=ty;
	}
      if(count>1)
	{
	  double a,b,c,z;
	  a=sqrt(pow(x[0]-x[1],2)+pow(y[0]-y[1],2));
	  b=sqrt(pow(x[1]-x[2],2)+pow(y[1]-y[2],2));
	  c=sqrt(pow(x[0]-x[2],2)+pow(y[0]-y[2],2));
	  z=(a+b+c)/2;
	  // cout<<a<<" "<<b<<" "<<c<<" "<<z<<endl;
	  ans+=sqrt(z*(z-a)*(z-b)*(z-c));
	}
      count++;
    }
  printf("%.6lf\n",ans);
}