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<stdio.h>
#include<math.h>
inline double SQ(double x){return x*x;}
int main(void)
{
	const int N = 20;
	double x[N],y[N],S=0,a,b,c,s;
	int n = 0;
	while(scanf("%lf,%lf",&x[n],&y[n]) == 2)
		++n;
	int i = 0, j = 1, k = n-1;
	while(i<j && j<k)
	{
		a = sqrt( SQ(x[i]-x[j])+SQ(y[i]-y[j]) );
		b = sqrt( SQ(x[j]-x[k])+SQ(y[j]-y[k]) );
		c = sqrt( SQ(x[k]-x[i])+SQ(y[k]-y[i]) );
		s = (a+b+c)/2;
		S += sqrt( s*(s-a)*(s-b)*(s-c) );
		
		if(j-i==1)
		{
			i = j;
			j = k-1;
		}
		else
		{
			k = j;
			j = i+1;
		}
	}
	printf("%f\n",S);

	return 0;
}