Don't take this the wrong way, but your inquiry is really useless. The bike you have is pre-owned...there's no telling if the previous owner(s) may have changed out the cassette, the chainrings, or the length of the rear derailleur...and thereby the chain as well. It all might not be original, or original spacs, to the bike. Likewise...the other owners of Allezs may have also made those changes...not to mention the chain length diffrence in various frame sizes. The best thing for you to do is to find (Google) a good chain length calculator and input the info from your bike to determine your proper chain length.

Dan