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<cstdio>
#include<cmath>
using namespace std;
typedef double D;

D len(D ax, D ay, D bx, D by){
  return sqrt( (ax-bx)*(ax-bx) + (ay-by)*(ay-by) );
}

D tri_area(D a, D b, D c){
  D s = (a+b+c)/2;
  return sqrt( s*(s-a)*(s-b)*(s-c) );
}

int main(){
  int n;
  D x[20], y[20];
  for(n=0;scanf("%lf,%lf",&x[n],&y[n])!=EOF;n++);

  D res = 0;
  for(int i=1;i<n-1;i++){
    res += tri_area(len(x[0],y[0],x[i],y[i]),
		    len(x[0],y[0],x[i+1],y[i+1]),
		    len(x[i],y[i],x[i+1],y[i+1]) );
  }
  printf("%.9lf\n",res);
}