How can I use Auto Number field as data type number in a formula?

How can I use Auto Number field as data type number in a formula?

I am trying to Round Robin accounts (not leads). I have an Auto Number field on accounts. Here's my formula:

${Accounts.AutoNumber} % 3

I believe the issue here is AutoNumber fields are text, not number. How can I change the value of this field to a number? Normally I could use VALUE() but I guess that function isn't available.