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 <cmath>
#include <string>
#include <cstdlib>
#include <strstream>
using namespace std;

int main (){
  double s,x1,y1,x2,y2,x3,y3,a,b,c,z;
  char ch;
  s=0;
  cin>>x1>>ch>>y1;
  cin>>x2>>ch>>y2;
  a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
  while(cin>>x3>>ch>>y3){
    b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
    c=sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
    z=(a+b+c)/2;
    s+=sqrt(z*(z-a)*(z-b)*(z-c));
    x2=x3;
    y2=y3;
    a=b;
  }
  cout<<s<<endl;
  
  return 0;
}