using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var regex = new Regex(@"(?=(?:^.{10,}$|(?<issmall>^.{6,9}$)))(?(issmall)(?=^.*\d)(?=^.*[a-zA-Z]).*|.*)", RegexOptions.Compiled);
 
		Console.WriteLine("0123456789: " + regex.IsMatch("0123456789"));
		Console.WriteLine("Hello1: " + regex.IsMatch("Hello1"));
		Console.WriteLine("Helloa: " + regex.IsMatch("Helloa"));
		Console.WriteLine("123456: " + regex.IsMatch("123456"));
		Console.WriteLine("Thats a very long text that should be accepted.: " + regex.IsMatch("Thats a very long text that should be accepted."));
	}
}

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