using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("A leap year is a year, occurring once every four years, that has 366 days including Feb. 29th as an intercalary day.");

        start:

        { Console.WriteLine("Please enter a year.");

        string input = Console.ReadLine();

        uint year;

        if(uint.TryParse(input, out year))

        if (year < 0)

          {Console.WriteLine("Please enter a positive number.");

           goto start;}

        {

            ulong leapyear = (year%4);

            if (year>3000)

            {

                Console.WriteLine("Don't look so far into the future.");

                goto start;

            }   

            if (year<1582)

            {

                Console.WriteLine("Please enter a more recent year because leap years only began in 1582.");

                goto start;

            }   

            else if (leapyear == 0)

            {

                Console.Clear();

                Console.WriteLine("This is a leap year.");

            }

            else

            {

                Console.Clear();

                Console.WriteLine("This is a common year.");

        }

        }

        }

    }

}

​