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 <stdio.h>
#include <math.h>
using namespace std;

int main() {
   int n=0,i;
   double x[20],y[20],a,b,c,s=0,z;
   while(scanf("%lf,%lf",&x[n],&y[n])!=EOF) n++;
   for (i=1;i<n-1;i++) {
	   a=sqrt((x[0]-x[i])*(x[0]-x[i])+(y[0]-y[i])*(y[0]-y[i]));
	   b=sqrt((x[0]-x[i+1])*(x[0]-x[i+1])+(y[0]-y[i+1])*(y[0]-y[i+1]));
	   c=sqrt((x[i]-x[i+1])*(x[i]-x[i+1])+(y[i]-y[i+1])*(y[i]-y[i+1]));
	   z=(a+b+c)/2;
	   s+=sqrt(z*(z-a)*(z-b)*(z-c));
   }
   cout << s << endl;
   return 0;
}