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.*;

public class Main {


    static double s(double a, double b, double c, double d) {
        return Math.abs(a * d - b * c) / 2;
    }

    static double[] p(String s) {
        String[] r = s.split(",");
        return new double[]{
                Double.parseDouble(r[0]),
                Double.parseDouble(r[1])
        };
    }

    public static void main(String... args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        double[] o = p(br.readLine());
        double[] a = p(br.readLine());
        double sum = 0.0;
        String line;
        while ((line = br.readLine()) != null) {
            double[] b = p(line);
            sum += s(a[0] - o[0], a[1] - o[1], b[0] - o[0], b[1] - o[1]);
            a[0] = b[0];
            a[1] = b[1];
        }
        System.out.println(sum);
    }
}