i am looking for assistance with a formula for data validation in a cell.

I have created a list of names that I am going to roatate by entering the top name in Cell A2 and that name will then go to the bottom of list.

I have the names in C3-C20 and I have the code in for that to work.  I however do not know what to put in A2 for the data validation.   I have searched and I am just not sure what to do.

thank you