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>

#define rep(i,n) for(int i=0;i<n;i++)

using namespace std;

int main()
{
	int count = 0;
	char c;
	double x[25],y[25];
	double ans = 0;
	while(cin >> x[count] >> c >> y[count])
	{
		count++;
	}

	x[count] = x[0];
	y[count] = y[0];

	rep(i,count)
	{
		ans += x[i]*y[i+1] - x[i+1]*y[i];
	}

	cout << abs(ans)/2.0 << endl;
	return 0;
}