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.util.*;

class Main {

    static Double areaTriangle (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) / 2.0;

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

    static void solve (ArrayList<Double> X, ArrayList<Double> Y) {
        int n = X.size();
        double area = 0;
        
        for(int i = 1; i <= n-2; i++) {
            area += areaTriangle(X.get(0), Y.get(0), X.get(i), Y.get(i), X.get(i+1), Y.get(i+1));
        }

        System.out.printf("%.7f\n", area);

    }

    public static void main (String [] args) {

        Scanner sc = new Scanner(System.in);
        ArrayList<Double> pointsX = new ArrayList<Double>();
        ArrayList<Double> pointsY = new ArrayList<Double>();

        while(sc.hasNext()) {
            String[] line = sc.nextLine().split(",");
            pointsX.add(Double.parseDouble(line[0]));
            pointsY.add(Double.parseDouble(line[1]));
        }

        solve(pointsX, pointsY);

    }
}