username

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] != "Sign")
            {
                if (command[0] == "Case")
                {
                    if (command[1] == "lower")
                    {
                        input = input.ToLower();
                    }
                    else
                    {
                        input = input.ToUpper();
                    }

                    Console.WriteLine(input);
                }
                if (command[0] == "Reverse")
                {
                    int start = int.Parse(command[1]);
                    int end = int.Parse(command[2]);

                    if ((start >= 0 && start < input.Length) && end >= 0 && end < input.Length)
                    {
                        string substring = input.Substring(start, end - start + 1);
                        char[] reverse = substring.Reverse().ToArray();
                        string output = new string(reverse);
                        Console.WriteLine(output);
                    }
                }
                if (command[0] == "Cut")
                {
                    if (input.Contains(command[1]))
                    {
                        int index = input.IndexOf(command[1]);
                        input = input.Remove(index, command[1].Length);
                        Console.WriteLine(input);
                    }
                    else
                    {
                        Console.WriteLine($"The word {input} doesn't contain {command[1]}.");
                    }
                }
                if (command[0] == "Replace")
                {
                    input = input.Replace(command[1], "*");
                    Console.WriteLine(input);
                }
                if (command[0] == "Check")
                {
                    if (input.Contains(command[1]))
                    {
                        Console.WriteLine("Valid");
                    }
                    else
                    {
                        Console.WriteLine($"Your username must contain {command[1]}.");
                    }
                }

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