SimpleTextEditor

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

namespace SimpleTextEditor
{
    class TextEditor
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var text = new StringBuilder();
            var stack = new Stack<string>();

            for (int i = 0; i < n; i++)
            {
                var parts = Console.ReadLine().Split();
                var command = int.Parse(parts[0]);

                switch (command)
                {
                    case 1:
                        text = text.Append(parts[1]);
                        stack.Push(text.ToString());
                        break;
                    case 2:
                        var erase = int.Parse(parts[1]);
                        text = text.Remove(text.Length - erase, erase);
                        stack.Push(text.ToString());
                        break;
                    case 3:
                        var charIndex = int.Parse(parts[1])-1;
                        Console.WriteLine(text.ToString().ToCharArray()[charIndex]);
                        break;
                    case 4:
                        if (stack.Count>1)
                        {
                            stack.Pop();
                            text = text.Clear();
                            text = text.Append(stack.Peek());
                        }
                        else if (stack.Count == 1)
                        {
                            stack.Pop();
                            text = text.Clear();
                        }
                        break;
                    default:
                        break;
                }
            }
        }
    }
}