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>
using namespace std;
int main(){
  double x[3],y[3],s=0,z,a,b,c;
  char cc;
  cin>>x[0]>>cc>>y[0];
  cin>>x[1]>>cc>>y[1];
  for(int i=1;cin>>x[i%2+1]>>cc>>y[i%2+1];i++){
    a = sqrt((x[1]-x[0])*(x[1]-x[0])+(y[1]-y[0])*(y[1]-y[0]));
    b = sqrt((x[2]-x[1])*(x[2]-x[1])+(y[2]-y[1])*(y[2]-y[1]));
    c = sqrt((x[2]-x[0])*(x[2]-x[0])+(y[2]-y[0])*(y[2]-y[0]));
    z = (a+b+c)/2;
    s += sqrt(z*(z-a)*(z-b)*(z-c));
  }
  printf("%.7f\n",s);
  return 0;
}