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 x1, double y1, double x2, double y2){
		double s = x1 * y2 - y1 * x2;
		s = s / 2;
		return s;
	}

	public void doIt(){
		Scanner sc = new Scanner(System.in);
		sc.useDelimiter("[, \\r\\n]+");

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

	}

}