Windscale Serpent + Brainstorm = 3 Counters?

[Peter_Rotten]

(this question is pulled from the single card discussion thread of Windscale Serpent)

If this is the final wording on Windscale Serpent,

The final wording is "Put a +1/+1 counter on *this* whenever a spell or ability causes you to draw a card"

...then how many counters does it get from Brainstorm?

3 or 1?

I've assumed 3.