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.*;
class Pair
{
	double x;
	double y;
	Pair(double x, double y)
	{
		this.x = x;
		this.y = y;
	}
}

public class Main 
{
	public static double helon(Pair p1, Pair p2, Pair p3)
	{
		double a = Math.sqrt((p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y));
		double b = Math.sqrt((p1.x - p3.x) * (p1.x - p3.x) + (p1.y - p3.y) * (p1.y - p3.y));
		double c = Math.sqrt((p2.x - p3.x) * (p2.x - p3.x) + (p2.y - p3.y) * (p2.y - p3.y));
		double z = (a + b + c) / 2;
		return(Math.sqrt(z * (z - a) * (z - b) * (z - c)));
	}
	
	public static void main(String[] args) 
	{
		Scanner stdIn = new Scanner(System.in);
		List<Pair> list = new ArrayList<Pair>();
		while(stdIn.hasNext())
		{
			String[] str = stdIn.next().split(",");
			double x = Double.parseDouble(str[0]);
			double y = Double.parseDouble(str[1]);
			list.add(new Pair(x, y));
		}
		double sum = 0;
		for(int i = 1; i < list.size() - 1; ++i)
		{
			sum += helon(list.get(0), list.get(i), list.get(i + 1));
		}
		System.out.println(sum);
	}
}