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 <iostream>
#include <complex>
#include <cmath>
#include <cstdio>
using namespace std;

int main() {
	typedef complex<double> xy;
	xy p[20];
	int n = 0;
	double x, y, s;
	while ( ~scanf( "%lf, %lf", &x, &y ) ) {
		p[n++] = xy( x, y );
	}
	for ( int i = 1; i < n - 1; i++ ) {
		s += ( conj( p[i] - p[0] ) * ( p[i + 1] - p[0] ) ).imag() / 2;
	}
	printf( "%.6f\n", abs(s) );
}