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.

<image>



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;

public class Main {
	static double dx[]=new double[19];
	static double dy[]=new double[19];
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		double x[]=new double[20];
		double y[]=new double[20];
		
		int i,k=0;
		double sum=0;
		while(sc.hasNext()){
			String str[]=sc.next().split(",");
			x[k]=Double.parseDouble(str[0]);
			y[k]=Double.parseDouble(str[1]);
			k++;
		}
		for(i=1;i<k;i++){
			dx[i-1]=x[i]-x[0];
			dy[i-1]=y[i]-y[0];
		}
		for(i=0;i+1<k-1;i++){
			sum+=area(dx[i],dy[i],dx[i+1],dy[i+1]);
		}
		System.out.printf("%.6f\n",sum);
	}
	public static double area(double a,double b,double c,double d){
		double s=a*d-b*c;
		if(s<0) s=s*(-1);
		return s/2;
	}
}