New to Access

I am new to Access. I am setting up a database for the museum I work for to track our members. Each of our members is assigned a 'Membership Number' that is formatted like this [INDENT]S72-0001[INDENT]S72-0002[INDENT]and so on

I am trying to find a way of having these numbers automatically generate in sequence for each new member. I have tried putting the "S72-" as a part of the label and simply setting the number as an AutoNumber, however Access 2010 does not allow you to have more then one AutoNumber.

Any help that can be provided would be greatly appreciated! Thanks!