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.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		List<Point> list = new ArrayList<Point>();
		while(sc.hasNext()) {
			String[] s = sc.next().split(",");
			list.add(new Point(Double.parseDouble(s[0]), Double.parseDouble(s[1])));
		}
		sc.close();
		double s = 0;
		for(int i = 1; i + 1 < list.size(); i++) {
			s += area(list.get(0), list.get(i), list.get(i + 1));
		}
		System.out.println(s);
	}
	static double area(Point p1, Point p2, Point p3) {
		return Math.abs((p1.x - p3.x) * (p2.y - p3.y) - (p2.x - p3.x) * (p1.y - p3.y)) / 2.0;
	}
	static class Point{
		double x, y;
		Point(double x, double y){
			this.x = x;
			this.y = y;
		}
	}
}