using System;

using System.Text;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(string.Join(",", SplitAlpha("H1N1")));

    }

​

    public static IEnumerable<string> SplitAlpha(string input)

    {

        var words = new List<StringBuilder>{new StringBuilder()};

        for (var i = 0; i < input.Length; i++)

        {

            words[words.Count - 1].Append(input[i]);

            if (i + 1 < input.Length && char.IsLetter(input[i]) != char.IsLetter(input[i + 1]))

            {

                words.Add(new StringBuilder());

            }

        }

​

        return words.Select(x => x.ToString());

    }

}