Demo

using System;
using System.Collections.Generic;
using System.Linq;

namespace Encapsulation
{
    class Program
    {
        static void Main(string[] args)
        {
            List<string> biscuits = Console.ReadLine()
                .Split(", ", StringSplitOptions.RemoveEmptyEntries)
                .ToList();

            string command = Console.ReadLine();

            while (command != "Eat")
            {
                string[] cmdArgs = command.Split();
                if (cmdArgs[0] == "Update-Any")
                {
                    for (int i = 0; i < biscuits.Count; i++)
                    {
                        if (biscuits[i] == cmdArgs[1])
                        {
                            biscuits[i] = "Out of stock";
                        }
                    }

                }
                else if (cmdArgs[0] == "Remove")
                {
                    int index = int.Parse(cmdArgs[2]);
                    if (index >= 0 && index < biscuits.Count)
                    {
                        biscuits[index] = cmdArgs[1];
                    }
                }
                else if (cmdArgs[0] == "Update-Last")
                {
                    biscuits[biscuits.Count - 1] = cmdArgs[1];
                }
                else if (cmdArgs[0] == "Rearrange")
                {
                    if (biscuits.Contains(cmdArgs[1]))
                    {
                        biscuits.Remove(cmdArgs[1]);
                        biscuits.Add(cmdArgs[1]);
                    }
                }

                command = Console.ReadLine();
            }

            List<string> output = biscuits.Where(x => x != "Out of stock").ToList();
            Console.WriteLine(string.Join(" ",output));
        }
    }
}