email validator

using System;
using System.Linq;
using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace _02._Boss_Rush
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();

            string[] command = Console.ReadLine().Split();

            while (command[0] != "Complete")
            {
                if (command[0] == "Make")
                {
                    if (command[1] == "Upper")
                    {
                        input = input.ToUpper();
                    }
                    else
                    {
                        input = input.ToLower();
                    }

                    Console.WriteLine(input);
                }
                if (command[0] == "GetDomain")
                {
                    int count = int.Parse(command[1]);

                    if (count >= 0 && count < input.Length)
                    {
                        char[] reverse = input.TakeLast(count).ToArray();
                        string output = new string(reverse);
                        Console.WriteLine(output);

                    }
                    else
                    {
                        Console.WriteLine(input);
                    }

                }
                if (command[0] == "GetUsername")
                {
                    if (input.Contains("@"))
                    {
                        int index = input.IndexOf("@");
                        string username = input.Substring(0, index);
                        Console.WriteLine(username);
                    }
                    else
                    {
                        Console.WriteLine($"The email {input} doesn't contain the @ symbol.");
                    }
                }
                if (command[0] == "Replace")
                {
                    input = input.Replace(command[1], "-");
                    Console.WriteLine(input);

                }
                if (command[0] == "Encrypt")
                {
                    char[] email = input.ToCharArray();

                    List<int> output = new List<int>();

                    foreach (int item in email)
                    {
                        output.Add(item);
                    }

                    Console.WriteLine(string.Join(" ", output));
                }

                command = Console.ReadLine().Split();
            }
        }
    }
}