C# Последовательность чисел - вывод по N-й элемент

C# Последовательность чисел - вывод по N-й элемент

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

namespace ConsoleApplication6
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Enter some number: ");
            string userText = Console.ReadLine();

            bool onlyDigits = true;
            int length = 30;

            foreach (var item in userText)
            {
                if (!Char.IsDigit(item))
                {
                    onlyDigits = false;
                    Console.WriteLine("\nWrong symbol: " + item + ". Only digits are allowed.\n");
                    break;
                }
            }

            if (!onlyDigits)
                Environment.Exit(0);
            else
                length = Convert.ToInt32(userText);            
            
            string[] sequence = new string[length];

            for (int i = 0; i < length; i++)
            {
                if (i == 0)
                {
                    sequence[0] = "1";   
                }
                else
                {
                    string new_item = "";

                    string str = sequence[i - 1];
                        
                    int symbolCount = 0;
                    char currentSymbol = '0';
                        
                    foreach (var item in str)
                    {
                        if (currentSymbol != item)
                        {
                            if (symbolCount > 0)
                            {
                                new_item = new_item + Convert.ToString(symbolCount) + currentSymbol;
                                symbolCount = 0;
                            }
                            currentSymbol = item;
                        }

                        symbolCount++;
                    }

                    if (symbolCount > 0)
                    {
                        new_item = new_item + Convert.ToString(symbolCount) + currentSymbol;
                        symbolCount = 0;
                    }

                    sequence[i] = new_item;

                }
            }

            for (int i = 0; i < sequence.Length; i++)
            {
                Console.Write(sequence[i]);

                if (i < sequence.Length - 1)
                    Console.Write(", ");
            }

            Console.Write("\n");
        }
    }
}