Import .as files from subdirectories

Hello,
my Flash project is beginning to get out of hand because there are too many .as files and I would like to organize them in folders. But I don’t know how I need to import them properly.

I put them in a folder called “levels”, in there is a Level.as and five specific files that extend the Level class, Ground0.as to Ground5.as.

I put the folder name levels as the package name, so for example the Level.as file begins as following

package levels{
    import flash.display.*;
    import flash.events.*;
    public class Level extends MovieClip {

and in my Document Class (“MainClass”), I tried to import the folder “levels”

package {
    import flash.display.*;
    import flash.events.*;
    import flash.utils.*;
    import flash.ui.Keyboard;
    import levels.*
    public class MainClass extends MovieClip {

but calling the classes that are in the subdirectory “levels” simply doesn’t work. Do I need to do something else or call the classes in a different way?

Thank you.