using System;
using System.Collections.Generic;
using System.IO;
using System.Text.RegularExpressions;
using System.Linq;
public class Test
{
	public static void Main()
	{
		var lst = new List<string> {"3.AAA", "AAA.BBB", "AAA.3.BBB", "AAA.3.B555B", "AAA.3.BBB.4", 
			"AAA.3.BBB.4.CCC", "AAA.3.BBB.CCC", "AAA.3.BBB.CCC.4", "AAA.3.BBB.CCC.4.DDD",
			"ZZZ.AAA.3.BBB","ZZZ.AAA.3.BBB.4","ZZZ.AAA.3.BBB.4.CCC", "ZZZ.AAA.3.BBB.CCC",
			"ZZZ.AAA.3.BBB.CCC.4", "ZZZ.AAA.3.BBB.CCC.4.DDD"};
		var rx = new Regex(@"^(?:(?!\d+\.)[^\s.]+\.)+\d+(?:\.(?!\d+(?=\.|$))[^\s.]+)+$", 
			RegexOptions.Compiled | RegexOptions.ECMAScript);
		foreach (var s in lst) 
		{
			if (rx.IsMatch(s))
				Console.WriteLine(s);
		}
	}
	
	
}