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 <complex>
#include <cstdio>
using namespace std;

int main(){
  int n=0;
  double x,y;
  complex<double> v[20];
  while(scanf("%lf,%lf",&x,&y)>0){
    v[n]=complex<double>(x,y);
    n++;
  }

  double s=0.0;
  for(int i=1;(i+1)<n;i++){
    s+=abs((conj(v[i]-v[0])*(v[i+1]-v[0])).imag())/2.0;
  }

  cout << s << endl;

  return 0;
}