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 <cmath>
#include <iomanip>
using namespace std;

int main()
{	
	double a, b, c, d, x, y, s = 0;
	char t;

	cin >> a >> t >> b >> c >> t >> d;

	while (cin >> x >> t >> y) {
		s += abs((c - a) * (y - b) - (d - b) * (x - a)) * 0.5;
		c = x;
		d = y;
	}

	cout << fixed << setprecision(6) << s << endl;

	return 0;
}