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.Scanner;

public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		Point2D.Double v1, v2, v3;
		String str[];
		double s;

		s = 0.0;
		str = sc.next().split(",");
		v1 = new Point2D.Double(Double.valueOf(str[0]), Double.valueOf(str[1]));
		str = sc.next().split(",");
		v2 = new Point2D.Double(Double.valueOf(str[0]), Double.valueOf(str[1]));
		while (sc.hasNext()) {
			str = sc.next().split(",");
			v3 = new Point2D.Double(Double.valueOf(str[0]), Double.valueOf(str[1]));
			double a = Math.sqrt(Math.pow(v2.x - v1.x, 2) + Math.pow(v2.y - v1.y, 2));
			double b = Math.sqrt(Math.pow(v3.x - v1.x, 2) + Math.pow(v3.y - v1.y, 2));
			double c = Math.sqrt(Math.pow(v3.x - v2.x, 2) + Math.pow(v3.y - v2.y, 2));
			double z = (a + b + c) / 2;
			s += Math.sqrt(z * (z - a) * (z - b) * (z - c));
			v2 = v3;
		}
		System.out.println(s);
	}
}