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

double cross_product(complex<double>, complex<double>);
int main(void) {
	complex<double> p[30];
	int n;
	double x, y, s = 0;

	n = 0;
	while (scanf("%lf,%lf", &x, &y) == 2) {
		p[n++] = complex<double>(x, y);
	}
	for (int i = n - 1; i >= 0; i--) {
		p[i] -= p[0];
	}
	for (int i = 2; i < n; i++) {
		s += cross_product(p[i - 1], p[i]);
	}
	if (s < 0) s = -s;
	cout << s/2 << endl;
	return 0;
}

double cross_product(complex<double> a, complex<double> b) {
	return (conj(a)*b).imag();
}