Tudy's Swim Tank

Tudy's all time, make-her-summer sport is swimming!  And she's all ready for swim camp next week!!! She's the 20th fastest and 20th slowest swimmer in the pool.  Now, assuming no two swimmers swim at the same speed, Tudygirls, how many swimmers are in Tudy's camp?

(Tudy's Tip:  39 swimmers and a host of reasons to love summer !!!  Check out Tudy's Fave suits just for you!)