using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(GetConsecutiveGroups("aaaabbccaa"));

    }

    private static string GetConsecutiveGroups(string input)

    {       

        var result = new StringBuilder();

        var sb = new StringBuilder();

        foreach (var c in input)

        {

            if (sb.Length == 0 || sb[sb.Length - 1] == c)

            {

                sb.Append(c);

            }

            else

            {

                result.Append($"{sb.Length}{sb[0]}");

                sb.Clear();

                sb.Append(c);

            }

        }

        if (sb.Length > 0)

        {

            result.Append($"{sb.Length}{sb[0]}");

        }

        return result.ToString();

    }

}