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.io.*;
public class Main {
	public static void main(String... args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String line = "";
		double x[] = new double[20];
		double y[] = new double[20];
		int i = 0;
		while ((line = br.readLine() ) != null){
			String numbers[] = line.split(",");
			x[i] = Double.parseDouble(numbers[0])-x[0];
			y[i] = Double.parseDouble(numbers[1])-y[0];				
			i++;
		}
		double area = 0;
		for (int k = 1; k<i; k++){
			area += x[k]*y[k+1]-x[k+1]*y[k];
		}
		System.out.println(Math.abs(area*0.5));
	}
}