Go deep into the Safari Zone and find Gold Teeth, then give them to the Warden (The guy with the bad speech) and he will give you the HM4.
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You need to have the HM4 Strength, obtained in the lost tower near Solacean town You need to have the 5th Gym badge, obtained in Hearthome City
thats not a game
In Nimbasa city I believe it is the 3rd house from the pokecenter when you are at the pokecenter there is a sign right by the house.
HM1 CUT HM2 FLY HM3 SURF HM4 STRENGTH HM5 FLASH HM6 ROCK SMASH HM7 WATERFALL HM8 DIVE --/ninjax/
from the lady at the top of the lost tower on route 209