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>

int n = 0;
double x[20], y[20];

int main()
{
	while( scanf( "%lf,%lf", &x[n], &y[n] ) != EOF )
		++n;

	double area = 0.0;
	for( int i = 0; i != n; ++i )
		area += x[i] * y[(i+1)%n] - y[i] * x[(i+1)%n];

	area /= 2.0;

	printf( "%.6f", std::abs( area ) );

	return 0;
}