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.awt.geom.Point2D;
import java.util.*;

public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = 0;
		double x, y, xp, yp, xq, yq;
		double a, b, c, z;
		double sum = 0;
		String[] s = new String[2];
		
		s = sc.next().split(",");
		x = Double.valueOf(s[0]);
		y = Double.valueOf(s[1]);
		s = sc.next().split(",");
		xp = Double.valueOf(s[0]);
		yp = Double.valueOf(s[1]);
		b = Point2D.Double.distance(x, y, xp, yp);
		
		while(sc.hasNext()){
			s = sc.next().split(",");
			xq = xp;
			yq = yp;
			xp = Double.valueOf(s[0]);
			yp = Double.valueOf(s[1]);
			
			a = b;
			b = Point2D.Double.distance(x, y, xp, yp);
			c = Point2D.Double.distance(xp, yp, xq, yq);
			
			z = (a+b+c)/2;
			sum += Math.sqrt(z*(z-a)*(z-b)*(z-c));
		}
		System.out.println(sum);
		
	}	
}