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 JAVA):

Solution:
import java.util.Scanner;

class Main
{
	public static void main(String args[])
	{
		Scanner sc = new Scanner(System.in).useDelimiter("[ ,\n]+");
		double S = 0.0;
		double x0 = sc.nextDouble(), y0 = sc.nextDouble();
		double xp = sc.nextDouble(), yp = sc.nextDouble();
		while (sc.hasNext())
		{
			double x = sc.nextDouble(), y = sc.nextDouble();
			double a = d(x0,y0,xp,yp),
				   b = d(xp,yp,x,y),
				   c = d(x,y,x0,y0);
			double z = (a + b + c) / 2.0;
			S += Math.sqrt(z * (z - a) * (z - b) * (z - c));
			
			xp = x;
			yp = y;
		}
		System.out.println(S);
	}
	private static double d(double xa, double ya, double xb, double yb)
	{
		return Math.sqrt((xa - xb) * (xa - xb) + (ya - yb) * (ya - yb));
	}
}