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:
//Area of Polygon
import java.io.*;

public class Main{
	public static void main(String[] args) throws Exception{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		double a,b,c,x1,x2,x3,y1,y2,y3,z,S=0;
		
		//???????????????????????±?????????
		String[] str1 = br.readLine().split(",");
		x1 = Double.parseDouble(str1[0]);
		y1 = Double.parseDouble(str1[1]);
		String[] str2 = br.readLine().split(",");
		x2 = Double.parseDouble(str2[0]);
		y2 = Double.parseDouble(str2[1]);
		String str = br.readLine();
		
		while(str != null){
			String[] str3 = str.split(",");
			x3 = Double.parseDouble(str3[0]);
			y3 = Double.parseDouble(str3[1]);
			a = Math.sqrt(Math.pow(x2-x1,2)+Math.pow(y2-y1,2));
			b = Math.sqrt(Math.pow(x3-x2,2)+Math.pow(y3-y2,2));
			c = Math.sqrt(Math.pow(x3-x1, 2)+Math.pow(y3-y1, 2));
			z = (a+b+c)/2;
			S += Math.sqrt(z*(z-a)*(z-b)*(z-c));
			str = br.readLine();
			x2 = x3;
			y2 = y3;
		}
		System.out.println(S);
		
		br.close();
	}
}