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 <cmath>
#include <cstdio>
#include <iostream>
int main(){
	double x0,y0,x1,y1,x, y, s = 0;
	char c;
	std::cin >> x0 >> c >> y0;
	x1 = x0; y1 = y0;
	while(std::cin>>x>>c>>y){
		s += x1*y - y1*x;
		x1 = x;
		y1 = y;
	}
	s += x1*y0 - y1*x0;
		printf("%.6f\n", fabs(s / 2));

}