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;
public class Main
{
	public static void main(String[] args) 
	{
		Scanner in=new Scanner(System.in);
		double x[]=new double[21];
		double y[]=new double[21];
		int i=0;
		double S=0;
		while(in.hasNext())
		{
			String s[]=in.next().split(",");
			x[i]=Double.valueOf(s[0]);
			y[i]=Double.valueOf(s[1]);
			i++;
		}
		x[i]=x[0];
		y[i]=y[0];
		for(int j=0;j<i;j++)
		{
			double seki=(x[j]-x[j+1])*(y[j]+y[j+1]);
			S+=seki;
		}
		System.out.printf("%.6f\n",Math.abs(S/2));
	}
}