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;

class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		double[][] p = new double[20][2];
		int n = 0;
		
		while(scan.hasNext()){
			String s[] = scan.next().split(",");
			p[n][0]=Double.parseDouble(s[0]);
			p[n][1]=Double.parseDouble(s[1]);
			n++;
		}
		
		double a = 0;
		
		for(int i = 0; i < n; i++){
			double x1 = p[i][0];
			double y1 = p[i][1];
			double x2 = p[(i + 1) % n][0];
			double y2 = p[(i + 1) % n][1];
			a += x1 * y2 - x2 * y1;
		}
		System.out.println(Math.abs(a / 2));
	}
}