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;

public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		double[][] pos = new double[20][2];
		int n = 0;
		while(stdIn.hasNext()){
			String[] a = stdIn.next().split(",");
			pos[n][0] = Double.parseDouble(a[0]);
			pos[n++][1] = Double.parseDouble(a[1]);
		}
		double sum = 0;
		for(int i=0;i<n-1;i++){
			sum += (pos[i][0]-pos[i+1][0])*(pos[i][1]+pos[i+1][1]);
		}
		sum += (pos[n-1][0]-pos[0][0])*(pos[n-1][1]-pos[0][1]);
		sum = sum/2;
		if(sum<0){
			sum *= -1;
		}
		System.out.printf("%.6f\n",sum);
	}
}