Has anybody seen "Last Summer" (1969)?

It's about three teenagers spending the summer at the beach out while folks are away and how a fourth, shy, sensitive awkward girl comes into their fold.  I only know bits and pieces of what happens and there's not much at all up on Youtube.  I don't even know if it's in print anymore.  Rex Reed and several others said that Catherine Burns, who played the shy outcast, was excellent.

 I would love to see it some time.