using System;

public class Program

{

    public static void Main()

    { var a = "aaaaabbbbcccc";

     var b = "";

     Console.WriteLine(a.Length);

        for(var i=a.Length-1; i>=1;i--)

        {

            if(a[i]!=a[i-1]){

                b+=a[i];

            }

        }

     Console.WriteLine(b);

    }

}