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

class Main {

    public static void main(String[] args) throws IOException {
        doit(args, System.in, System.out);
    }

    static void doit(String[] args, InputStream in, PrintStream out)
            throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        String line = null;
        double[][] points = new double[21][2];
        int n = 0;
        while ((line = reader.readLine()) != null) {
            if (line.isEmpty()) {
                continue;
            }
            String[] values = line.split(",");
            points[n][0] = Double.parseDouble(values[0]);
            points[n][1] = Double.parseDouble(values[1]);
            n++;
        }
        points[n][0] = points[0][0];
        points[n][1] = points[0][1];
        double s = 0.0;
        for (int i = 0; i < n; i++) {
            s += 0.5 * (points[i][0] * points[i + 1][1] - points[i + 1][0]
                    * points[i][1]);
        }
        out.println(Math.abs(s));
    }
}