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 {
	private Scanner sc;

	public static void main(String[] args) {
		new Main();
	}
	
	public Main() {
		sc = new Scanner(System.in);

		String[] nico = sc.nextLine().split(",");
		double fx = Double.parseDouble(nico[0]);
		double fy = Double.parseDouble(nico[1]);

		nico = sc.nextLine().split(",");
		double ox = Double.parseDouble(nico[0]);
		double oy = Double.parseDouble(nico[1]);
		
		double s = 0.0;
		while (sc.hasNextLine()) {
			nico = sc.nextLine().split(",");
			double tx = Double.parseDouble(nico[0]);
			double ty = Double.parseDouble(nico[1]);

			double a = Math.sqrt((fx - ox) * (fx - ox) + (fy - oy) * (fy - oy));
			double b = Math.sqrt((fx - tx) * (fx - tx) + (fy - ty) * (fy - ty));
			double c = Math.sqrt((ox - tx) * (ox - tx) + (oy - ty) * (oy - ty));
			double z = (a + b + c) / 2;
			
			s = s + Math.sqrt(z * (z - a) * (z - b) * (z - c));
			
			ox = tx;
			oy = ty;
		}
		
		System.out.println(s);
	}
}