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.*;
import java.io.*;

public class Main{
	public static void main(String[] args){
		Scanner stdIn = null;
		List<Double> point = new ArrayList<Double>();
		
		try{
			stdIn = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
			while( stdIn.hasNext() ){
				String str = stdIn.next();
				String[] s = str.split(",");
				double x = Double.parseDouble(s[0]);
				double y = Double.parseDouble(s[1]);
				point.add(x);
				point.add(y);
			}
			double sum = 0;
			for(int i = 2; i < point.size()/2; i++){
				double x = point.get(2*i)-point.get(0);
				double y = point.get(2*i+1)-point.get(1);
				double a = Math.sqrt(x*x+y*y);
				x = point.get(2*i-2)-point.get(0);
				y = point.get(2*i-1)-point.get(1);
				double b = Math.sqrt(x*x+y*y);
				x = point.get(2*i-2)-point.get(2*i);
				y = point.get(2*i-1)-point.get(2*i+1);
				double c = Math.sqrt(x*x+y*y);
				double z = (a+b+c)/2;
				sum += Math.sqrt(z*(z-a)*(z-b)*(z-c));
			}
			System.out.printf("%.6f", sum);
		} finally {
			if( stdIn != null){
				stdIn.close();
			}
		}
	}
}