using System;

public class Program

{

    public static void Main()

    {

        var s = $"0001000236818110000017346000 ";

        Console.WriteLine(s.Substring(11,6));   //Should be T

        Console.WriteLine(s.Left(2));   //Should be Tu

        Console.WriteLine(s.Left(3));   //Should be Tur

        Console.WriteLine(s.Left(4));   //Should be Turk

        Console.WriteLine(s.Left(5));   //Should bet Turke

        Console.WriteLine(s.Left(6));   //Should be Turkey

        Console.WriteLine(s.Left(7));   //Should be Turkey (already pass the string length)

        Console.WriteLine(s.Left(100)); //Should be Turkey (already pass the string length)

    }

}

​

public static class StringExtensions

{

    public static string PermissiveSubstring(this string input, int startIndex, int length)

    {       

        var output = input.Substring(startIndex, input.Length - startIndex <= length ? input.Length-startIndex: length);

        return output;

    }

    public static string Left(this string input, int length)

    {

        return input.PermissiveSubstring(11, length);

    }

    public static string Right(this string input, int length)

    {

        var output = input.Reverse().PermissiveSubstring(0, length).Reverse();

        return output;

    }

    public static string Reverse(this string s)

    {

        char[] charArray = s.ToCharArray();

        Array.Reverse( charArray );

        return new string( charArray );

    }

}