Silly question

Hello guys!
My friend and I are writing her university project work, and as part of it are supposed to translate a chapter from any Harry Potter book. We chose "HP and the Philosopher's stone", and now we're having difficulty with the following:

"Hagrid must have forgotten to tell him something, like tapping the third brick on the left to get into Diagon alley".

Where exactly do you find this third brick on the left? Do you count bricks from the place where you are standing or from the left end of the wall?

(please state what country you are from, we found this important while asking our English-speaking pals)