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 scan = new Scanner(System.in);
        String str = "";
        while(scan.hasNext()){
        	str += scan.next() + " ";
        }
        String[] nstr = str.split(" ");
        int n = nstr.length;
        double[][] point = new double[n][2];
        for(int i = 0;i < n;i++){
        	String[] s = nstr[i].split(",");
        	point[i][0] = Double.parseDouble(s[0]);
        	point[i][1] = Double.parseDouble(s[1]);
        }
        double sum = 0;
        for(int i = 1;i < n-1;i++){
        	double a = Math.sqrt((point[0][0] - point[i][0])*(point[0][0] - point[i][0])
        			+(point[0][1] - point[i][1])*(point[0][1] - point[i][1]));
        	double b = Math.sqrt((point[0][0] - point[i+1][0])*(point[0][0] - point[i+1][0])
        			+(point[0][1] - point[i+1][1])*(point[0][1] - point[i+1][1]));
        	double c = Math.sqrt((point[i][0] - point[i+1][0])*(point[i][0] - point[i+1][0])
        			+(point[i][1] - point[i+1][1])*(point[i][1] - point[i+1][1]));
        	double z = (a + b + c) / 2.0;
        	sum += Math.sqrt(z*(z-a)*(z-b)*(z-c));
        }
        System.out.printf("%.6f\n",sum);
    }
}