Der Philosoph (1989)

A philosopher discovers the true meaning of life when he movies in with three sexually adventurous sisters in Der Philosoph (1989). Broke and ignored by his more high-profile peers, philosopher Georg (Johannes Herrschmann) is on the verge of retreating from the world to concentrate on more esoteric matters. But then he meets Franziska (Adriana Altaras), Beate (Friederike Tiefenbacher) and Martha (Claudia Matschulla), sisters who share everything-- the work together, they live together, and even *ahem* enjoy each others' lovers. These generous gals invite Georg to move in with them, and soon he's got more than Socrates and Descartes on his mind. And with full nudity from Adriana and Friederike and bare boobs from Claudia, you'll be proclaiming-- "It's pink, therefore a clam!"