How many 18" S4 alloys do you get as standard?

[18ME]

I've just bought 4 new S4 wheels for my A4 but what do I do regarding the spare? I've got 17" 5 star alloys on at the moment and wasn't sure wether to sell the five or keep one as a spare or is there an alternative foam type set that you can use.

Cheers
Martin