How do you move boulders in Pokemon Pokemon LeafGreen?

How do you move boulders in Pokemon:

LEAF GREEN - FIRE RED - YELLOW

To move boulders you have to learn a HIDDEN MOVE (HM)called STRENGTH.

You get this HIDDEN MOVE (HM) by giving the Warden in Fushia City his

Gold Teeth back.

You can find his teeth in the Safari Zone, close to the Secret House.

The Warden lives at the east-side of Fushia in a house with a pond behind it.