Simple Text Editor

using System;
using System.Text;
using System.Collections.Generic;

namespace Simple_Text_Editor
{
    class Program
    {
        static void Main()
        {
            var sb = new StringBuilder();
            var addComm = new Stack<int>();
            var remComm = new Stack<string>();
            var stack = new Stack<int>();
            var n = int.Parse(Console.ReadLine());
            for (int i = 0; i < n; i++)
            {
                var input = Console.ReadLine()
                    .Split();
                var com = input[0];
                switch (com)
                {
                    case "1":
                        {
                            var arg = input[1];
                            sb.Append(arg);
                            addComm.Push(arg.Length);
                            stack.Push(1);
                        }
                        break;
                    case "2":
                        {
                            var arg = int.Parse(input[1]);
                            var start = sb.Length - arg ;
                            remComm.Push(sb.ToString(start, arg));
                            sb.Remove(start, arg);
                            stack.Push(2);
                        }
                        break;
                    case "3":
                        {
                            var arg = int.Parse(input[1])-1;
                            Console.WriteLine(sb[arg]);
                        }
                        break;
                    case "4":
                        {
                            var uncom = stack.Pop();
                            switch (uncom)
                            {
                                case 1:
                                    {
                                        var rem = addComm.Pop();
                                        var start = sb.Length - rem;
                                        sb.Remove(start, rem);
                                    }
                                    break;
                                case 2:
                                    {
                                        var add = remComm.Pop();
                                        sb.Append(add);
                                    }
                                    break;
                            }
                        }
                        break;
                }
            }
        }
    }
}