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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main{
	public static void main(String[] args)throws IOException{
		InputStreamReader isr = new InputStreamReader(System.in);
		BufferedReader reader = new BufferedReader(isr);
		double[] x = new double[20];
		double[] y = new double[20];
		int i = 0;
		String string;
		
		while((string = reader.readLine()) != null){
			x[i] = Double.valueOf(string.split(",")[0]);
			y[i] = Double.valueOf(string.split(",")[1]);
			i++;
		}
		
		double a = Math.hypot(x[1] - x[0], y[1] - y[0]);
		double b = Math.hypot(x[2] - x[0], y[2] - y[0]);
		double c = Math.hypot(x[2] - x[1], y[2] - y[1]);
		double z = (a + b + c) / 2;
		double S = Math.sqrt(z * (z - a) * (z - b) * (z - c));
		for(int j = 2; j < i - 1; j++){
			a = Math.hypot(x[j] - x[0], y[j] - y[0]);
			b = Math.hypot(x[j + 1] - x[0], y[j + 1] - y[0]);
			c = Math.hypot(x[j + 1] - x[j], y[j + 1] - y[j]);
			z = (a + b + c) / 2;
			S += Math.sqrt(z * (z - a) * (z - b) * (z - c));
		}
		System.out.println(S);
	}
}