isPrime (C# Shell App Paste)

//Disclaimer: The creator of 'C# Shell (C# Offline Compiler)' is //in no way responsible for the code posted by any user.
using System;
using System.IO;
using System.Linq;
using System.Collections.Generic;

namespace IsPrime
{

    public class IsPrime
    {
        public static void Main()
        {
            Console.WriteLine("Въведи просто число");
            ulong n = ulong.Parse(Console.ReadLine());
            Console.WriteLine(isPrime(n));
        }

        public static  bool isPrime(ulong n)
        {
            if(n <= 3)
            {
                return n > 1;
            }
            else if(n % 2 == 0 || n % 3 == 0)
            {
                return false;
            }

            for(ulong i = 5; i*i < n;i += 6)
            {
                if (n %i == 0 || n % (i+2) == 0)
                {
                    return false;
                }
            }
            return true;

        }
    }
}