>>527886925
Don't mind >>527891673, I just woke up from a nap and I needed to wind up the brain first.

The probability for getting the banner skin is 1.5% (3% for 5 star with 50% being the banner skin). If you want to +5 you need it 6 times, not 5 as I previously thought because it actually starts at 0 and goes to +1, +2, +3, +4, +5. So the 334 is actually wrong. Anyway:
Negative binominal distribution is k/p where k is the amount you want and p is the probability.
k = 6 (if you want +5)
p = 0.015 (1.5% per pull)
6 / 0.015 = 400
So you need 400 pulls instead of my previous false advertisement of 334.