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;
int main(void)
{	
	double x[20],y[20],s,z,ss,l1,l2,l3;
	int i,j,n;
	n=0;
	while(scanf("%lf,%lf",&x[n],&y[n])!=EOF) n++;
	s=0.0;
	for(i=1;i<n-1;i++)	{
		l1=sqrt((x[0]-x[i])*(x[0]-x[i])+(y[0]-y[i])*(y[0]-y[i]));
		l2=sqrt((x[0]-x[i+1])*(x[0]-x[i+1])+(y[0]-y[i+1])*(y[0]-y[i+1]));
		l3=sqrt((x[i+1]-x[i])*(x[i+1]-x[i])+(y[i+1]-y[i])*(y[i+1]-y[i]));
		z=(l1+l2+l3)/2.0;
		ss=sqrt(z*(z-l1)*(z-l2)*(z-l3));
		s+=ss;
	}
	printf("%lf\n",s);
	return 0;
}