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.*;
import java.util.*;

class Main{
    public static void main(String[] args){
	BufferedReader sc=new BufferedReader(new InputStreamReader(System.in));
	try {
	    String st;
	    ArrayList<Double> x, y;
	    x = new ArrayList<Double>();
	    y = new ArrayList<Double>();
	    while((st=sc.readLine())!=null){
		String[] sp = st.split(",");
		x.add(Double.valueOf(sp[0]));
		y.add(Double.valueOf(sp[1]));
	    }
	    double sum1 = x.get(x.size()-1)*y.get(0), sum2 = x.get(0)*y.get(y.size()-1);;
	    for(int i=0; i<x.size()-1; i++){
		sum1+=x.get(i)*y.get(i+1);
		sum2+=x.get(i+1)*y.get(i);
	    }
	    System.out.println(Math.abs(sum1-sum2)/2.0);
	}catch(Exception e){
	    System.out.println("Error");
	}
    }
}