how to Skip unauthorized access directory and moving to next directory to search all the".txt"?

Question

I am trying to search all ".txt" file for a drive (C:). For that I am searching "AllDirectories" of drive C:, but I am getting exception while some directory access is denied and my program terminates.

try
            {
                var filename = Directory.GetFiles("C:\\", "*.txt", SearchOption.AllDirectories);
                Console.WriteLine(filename.ToString());
                foreach (string a in filename)
                {

                    Console.WriteLine(a);
                }
            }
            catch (Exception ex) { Console.WriteLine(ex); }

System.UnauthorizedAccessException: Access to the path 'C:\Documents and Settings' is denied.

How to skip unauthorized access directory and moving to next directory to search all the".txt"?

Exception:

System.UnauthorizedAccessException: Access to the path 'C:\Documents and Settings' is denied. at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.FileSystemEnumerableIterator1.HandleError(Int32 hr, String path) at System.IO.FileSystemEnumerableIterator1.AddSearchableDirsToStack(SearchData localSearchData) at System.IO.FileSystemEnumerableIterator1.MoveNext() at System.Collections.Generic.List1..ctor(IEnumerable`1 collection) at System.IO.Directory.InternalGetFileDirectoryNames(String path, String userPathOriginal, String searchPattern, Boolean includeFiles, Boolean includeDirs, SearchOption searchOption, Boolean checkHost) at System.IO.Directory.InternalGetFiles(String path, String searchPattern, SearchOption searchOption) at System.IO.Directory.GetFiles(String path, String searchPattern, SearchOption searchOption) at ConsoleApp1.Program.Main(String[] args) in c:\users\h190733\source\repos\ConsoleApp1\ConsoleApp1\Program.cs:line 16