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.

Ex Input:
metis is the goddess of wisdom in greek mythology.

Ex Output:
metis

Ex Input:
diana ross is a famous american soul and pop singer.

Ex Output:
diana ross

Ex Input:
the horst-wessel-lied ("horst wessel song"), also known as "die fahne hoch" ("the flag on high", from its opening line), was the anthem of the nazi party from 1930 to 1945.

Ex Output:
horst-wessel-lied