PasswordReset-ExamPreparation

using System;
using System.Text;

namespace PasswordReset
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();
            StringBuilder oldSbPassword = new StringBuilder(input);
            StringBuilder newSbPassword = new StringBuilder();

            string command = string.Empty;
            while ((command = Console.ReadLine()) != "Done")
            {
                string[] commandArray = command.Split();
                if (commandArray[0] == "TakeOdd")
                {
                    for (int i = 0; i <= oldSbPassword.Length - 1; i++)
                    {
                        if (i % 2 != 0)
                        {
                            newSbPassword.Append(oldSbPassword[i]);
                        }
                    }

                    Console.WriteLine(newSbPassword);
                    oldSbPassword = newSbPassword;
                }

                else if (commandArray[0] == "Cut")
                {
                    int index = int.Parse(commandArray[1]);
                    int validCurrentIndex = Math.Max(0, index);
                    int validIndex = Math.Min(oldSbPassword.Length - 1, validCurrentIndex);
                    int length = int.Parse(commandArray[2]);
                    int validLength = Math.Max(0, length);
                    int validCurrentLength = Math.Min(length, (oldSbPassword.Length - validCurrentIndex));

                    oldSbPassword.Remove(validCurrentIndex, validCurrentLength);
                    Console.WriteLine(oldSbPassword);
                }

                else if (commandArray[0] == "Substitute")
                {
                    string substring = commandArray[1];
                    string substitute = commandArray[2];

                    if (oldSbPassword.ToString().Contains(substring) && substitute != substring)
                    {
                        oldSbPassword.Replace(substring, substitute);
                        Console.WriteLine(oldSbPassword);
                    }

                    else if (oldSbPassword.ToString().Contains(substring) && substitute == substring)
                    {
                        Console.WriteLine("Nothing to replace!");
                    }

                    else if (oldSbPassword.ToString().Contains(substring) == false)
                    {
                        Console.WriteLine("Nothing to replace!");
                    }
                }
            }

            Console.WriteLine($"Your password is: {oldSbPassword}");
        }
    }
}