What sized aquarium for 2 clownfish?

Okay, I was thinking about getting into saltwater aquariums, all I want in my aquarium is the live rock, 2 peppermint shrimp and two clownfish, I don't know which ones, they are like the maroon ones, but they have an orange head, maybe they are hybrids, but the fish store near me has them all the time. The clownfish are really small (I.e. young) so I don;t have any idea about what size they are as adults, can anyone tell me what sized aquarium I should get? And I can't get like a 55 gallon or something because I won't have that much room in my new apartment.