Where do you get HM strength in Pokemon Red?

To get Strength (HM04) in Pokemon Red, you must travel to Fuchsia City. When there, you must venture deep into the Safari Zone, all the way to the last area with the secret house. In that area the GOLD TEETH are lying on the ground just inside by the door. Get them and bring them to the Warden back in the city. (He lives in a cottage next to the Pokemon Center.) He will give you HM04.