The Classic Fedora is a hat found on the first floor of the Clothing Store. It can be purchased for a mere 52 Bucks. After purchasing it, you'll only be able to wear it in Adopt Me!, unless you buy it on the actual Roblox Catalog.
On the Roblox Catalog, this hat's description reads:

A black felt fedora. Ideal for 1920s journalists, detectives, and Linux hackers. This hat demonstrates good taste and exudes class.