judge ми дава 90/100

Ето решениетто ми:

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

namespace Final_Exam_Retake___9_August_2019_Username
{
    class Program
    {
        static void Main(string[] args)
        {
            string userName = Console.ReadLine();

            string input = Console.ReadLine();

            while (input!= "Sign up")
            {
                string[] commands = input.Split(" ");

                string command = commands[0];

                if(command== "Case")
                {
                    string casees = commands[1];
                    if(casees== "lower")
                    {
                        userName = userName.ToLower();
                        Console.WriteLine(userName);
                    }
                    else
                    {
                        userName = userName.ToUpper();
                        Console.WriteLine(userName);
                    }
                }
                else if(command== "Reverse")
                {
                    int startIndex = int.Parse(commands[1]);
                    int endIndex = int.Parse(commands[2]);

                    if (startIndex >= 0 && startIndex < userName.Length&& endIndex > startIndex && endIndex < userName.Length)
                    {
                        int startIndexes = userName.IndexOf(userName[startIndex]);
                        int endIndexes = userName.LastIndexOf(userName[endIndex]);
                        int length = endIndexes - startIndexes + 1;
                        string word = userName.Substring(startIndexes,length);                           
                            Console.WriteLine(string.Join("", word.Reverse()));                                              
                    }
                }
                else if(command== "Cut")
                {
                    string word = commands[1];
                    if (userName.Contains(word))
                    {
                        userName = userName.Remove(userName.IndexOf(word), word.Length);
                        Console.WriteLine(userName);
                    }
                    else
                    {
                        Console.WriteLine($"The word {userName} doesn't contain {word}.");
                    }
                }
                else if(command== "Check")
                {
                    string word = commands[1];
                    if (userName.Contains(word))
                    {
                        Console.WriteLine("Valid");
                    }
                    else
                    {
                        Console.WriteLine($"Your username must contain {word}.");
                    }
                }
                else if(command== "Replace")
                {
                    string replacement = commands[1];
                    userName = userName.Replace(replacement, "*");
                    Console.WriteLine(userName);
                }
                input = Console.ReadLine();
            }
        }
    }
}