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 {

	private double getS(double a, double b, double c){

		double z = (a + b + c) / 2;
		double s = z * (z - a) * (z - b) * (z - c);
		s = Math.sqrt(s);
		return s;
	}

	public void doIt(){
		Scanner sc = new Scanner(System.in);
		sc.useDelimiter("[, \\r\\n]+");
		ArrayList<Point2D> list = new ArrayList<Point2D>();
		while(sc.hasNext()){
			list.add(new Point2D.Double(sc.nextDouble(), sc.nextDouble()));
		}
		double sum =0;
		int len = list.size();
		Point2D start = list.get(0);
		for(int i=1; i < len; i++ ){
			sum += getS(list.get(i).distance(start), list.get((i+1) % len).distance(start), list.get((i+1) % len).distance(list.get(i)));
		}
		System.out.printf("%1.6f\n",sum);
	}
	public static void main(String[] args) {
		Main obj = new Main();
		obj.doIt();

	}

}