Find Duplicate rows

Hey guys I have kind of an easy one, but i really can't figure out how to make a forumla work for this

Basically i have data with two columns with header rows First Name, Last Name. It is a long list of customers which I am trying to find duplicates.

I basically need a simple formula that i can drop into C2 that will check for duplicate rows and display "Duplicate" or "No Duplicate" and that i can fill down

Any help with this will be greatly appreciated, as there is over 5000 customers on this list, and manual scanning will be quite a daunting task