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 static java.lang.Math.*;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        List<Double[]> l = new ArrayList<>();
        while (sc.hasNext()) {
            Double[] p = Stream.of(sc.next().split(",")).map(Double::parseDouble).toArray(Double[]::new);
            l.add(p);
        }
        double area = 0;
        for (int i = 0; i < l.size() - 2; i++) {
            double a = sqrt(pow(l.get(i + 1)[0] - l.get(i)[0], 2) + pow(l.get(i + 1)[1] - l.get(i)[1], 2));
            double b = sqrt(pow(l.get(l.size() - 1)[0] - l.get(i + 1)[0], 2) + pow(l.get(l.size() - 1)[1] - l.get(i + 1)[1], 2));
            double c = sqrt(pow(l.get(i)[0] - l.get(l.size() - 1)[0], 2) + pow(l.get(i)[1] - l.get(l.size() - 1)[1], 2));
            double z = (a + b + c) / 2;
            area += sqrt(z * (z - a) * (z - b) * (z - c));
        }
        System.out.println(area);
    }
}