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

class Main {
    static double calcArea(double x1, double y1, double x2, double y2, double x3, double y3) {
        double a = Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
        double b = Math.sqrt((x2 - x3) * (x2 - x3) + (y2 - y3) * (y2 - y3));
        double c = Math.sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1));
        double z = (a + b + c) / 2;

        return Math.sqrt(z * (z - a) * (z - b) * (z - c));
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(",");
        double x1 = Double.parseDouble(s[0]);
        double y1 = Double.parseDouble(s[1]);
        double area = 0;

        s = br.readLine().split(",");
        double befx = Double.parseDouble(s[0]);
        double befy = Double.parseDouble(s[1]);

        String line;
        while ((line = br.readLine()) != null) {
            String[] second = line.split(",");
            double nowx = Double.parseDouble(second[0]);
            double nowy = Double.parseDouble(second[1]);

            area += calcArea(x1, y1, befx, befy, nowx, nowy);

            befx = nowx;
            befy = nowy;
        }

        System.out.printf("%.6f%n", area);
    }
}