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 <bits/stdc++.h>
using namespace std;
typedef complex<double> xy_t; 
xy_t p[22];
char c;
double x, y;
double sum;
int n;
int main()
{
	sum=0.0;
	n=0;
	//while(scanf("%lf,%lf", &x, &y)!=EOF)
	while(cin >> x >> c >> y)
	{
		n++;
		p[n]=xy_t(x, y);
	}
	p[n+1]=p[1];
	for(int i=1; i<=n; i++)
	{
		sum+=(conj(p[i])*p[i+1]).imag()/2;
	}
	cout << abs(sum) << endl;
	return 0;
}