public static void UserInterface()
        {
            Console.Clear();
            Console.WriteLine("-----------------------------------------------------------------\n");
            Console.WriteLine("\t  PASSWORD AUTHENTICATION SYSTEM\n");
            Console.WriteLine("\t  Please select one option");
            Console.WriteLine("\t  1. Establish an account");
            Console.WriteLine("\t  2. Authenticate a user");
            Console.WriteLine("\t  3. Exit the system\n");
            Console.Write("\t  Enter Selection:  ");
            string userInput = Console.ReadLine();

            Console.WriteLine("\n-----------------------------------------------------------------");

            if (userInput == "1")
            {
                Console.Write("Enter a desired user name: ");
                string userName = Console.ReadLine();
                if (!userList.Contains(userName))
                {
                    userList.Add(userName);
                    Console.Write("Enter a desired password: "******"This username is unavailable");
                }
            }
            if (userInput == "2")
            {
                Console.Write("Enter your user name: ");
                string userName = Console.ReadLine();
                Console.Write("Enter the password: "******"User {userName} has been authenticated");
                    Console.WriteLine($"  User name = {userName}");
                    Console.WriteLine($"  Password = {userPassword}");
                    Console.WriteLine($"  Encrypted Password = {u[userName]}");
                }
                else
                {
                    Console.WriteLine("Username / Password invalid.");
                }
            }
            if (userInput == "3")
            {
                Console.WriteLine("\nHere is a list of all the users");
                for (int i = 0; i < userList.Count; i++)
                {
                    Console.WriteLine($"  [{userList[i]}, {u[userList[i]]}]");
                }
                Console.WriteLine("\nErasing all user accounts.");
                Console.WriteLine("See you later alligator");
                return;
                // Wait some time then close application
            }
            if (userInput == "Access_Admin_Controls")
            {
                u["Admin"] = "qwerty123456";
                Console.Write("Enter the password: "******"Admin"])
                {
                    Console.WriteLine("Access Granted.");
                    AdminInterface();
                }
            }
            if (userInput != "1" && userInput != "2" && userInput != "3" && userInput != "Access_Admin_Controls")
            {
                Console.WriteLine("\nOnly 1, 2, and 3 are correct inputs. Please select one of those numbers.\n");
            }
            Console.WriteLine("\nPress any key to continue.");
            Console.ReadKey();
            UserInterface();
        }