Ei, guys, what's up?

I'm trying to find a formula that returns the last valid number in a column.
What i learned so far is a formula that works only if there's no empty cell in the column.

I mean,

A1 5
A2 7
A3
A4 8
A5 4

A formula that returns "4" as answar, no "7".
Sorry for being a noob in excel. I'm just a beginner. Sorry for that bad english too. I'm brazilian.
Thanks for now.