using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string input = "aaaabbbccdaa"; // "a4b3c2da2"

        string output= string.Empty;

        IEnumerable<string> lstOutput= new IEnumerable<string>();

        char[] inputChar= input.ToCharArray();

        for(int i= 0 ; i <= inputChar.Length; i++)

        {

            output= output + inputChar[i];

            lstOutput.Add(output);  

        }

        Console.WriteLine(lstOutput);

    }

}