using System;

public class Program

{

    public static double Add(double x = 2, double y = 1) {

        return x + y;

    }

    public double Multiply(double x, double y) {

        return x * y;

    }

    public static double Multiply(double x, double y, double z) {

        return x * y * z;

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

        double result = Add(4, 5.7);

        Console.WriteLine(result);

        double resultFromMultiply = Multiply(1, 2, 3);

        Console.WriteLine(resultFromMultiply);

    }

}