Using IF Function in Formula Field

Using IF Function in Formula Field

Trying to return something other than the 1 (true) or 0 (false). Seems simple enough but I am stumped.

If(${Contacts.Sales YTD}>75000,'Gold',(If(${Contacts.Sales YTD}>55000,'Silver',(If(${Contacts.Sales YTD}>35000,'Bronze','Not Rated')))))