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.Path2D;
import java.awt.geom.Point2D;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Main{
	public static void main(String args[])throws IOException{
		Path2D.Double path = new Path2D.Double();;
		Point2D.Double[] p = new Point2D.Double[20];
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String line;
		String[] splitLine = new String[2];
		int count=0;
		double a,b,c,z;
		double sum=0;
		
		for(int i=0;i<20;i++){
			p[i] = new Point2D.Double();
		}
		
		while(true){
			line = br.readLine();
			if(line == null || line.isEmpty())
				break;
			splitLine = line.split(",");
			p[count].setLocation(Double.parseDouble(splitLine[0]),Double.parseDouble(splitLine[1]));
			count++;
		}
		
		for(int i=0;i<count-2;i++){
			a=p[0].distance(p[i+1]);
			b=p[i+1].distance(p[i+2]);
			c=p[i+2].distance(p[0]);
			z=(a+b+c)/2;
			sum+=Math.sqrt(z*((z-a)*(z-b)*(z-c)));
		}
		
		System.out.printf("%.6f\n",sum);
	}
}