Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Input: Consider Input: aesthetics is a branch of philosophy.

Output: aesthetics


Input: Consider Input: in greek mythology, the nereids ( "nereides") are sea nymphs, the fifty daughters of nereus, the old man of the sea, and the okeanid doris.

Output: nereid


Input: Consider Input: the pittsburgh symphony orchestra (pso) is an american orchestra based in pittsburgh, pennsylvania.


Output: pittsburgh symphony orchestra