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.

<image>



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()
{

	char c; int f=0;
	double s,x,y,x0,y0,vx[2],vy[2];

	cin >> x0 >> c >> y0;
	cin >> x  >> c >> y ;

	vx[1] = x-x0;
	vy[1] = y-y0;

	s=0;
	while(cin >> x >> c >> y)
	{
		vx[f] = x-x0;
		vy[f] = y-y0;
		
		s+= fabs(vx[f]*vy[1-f] - vx[1-f]*vy[f]);
		
		f=1-f;
	}

	cout << s/2.0 << endl;
}