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:
the wii u is a video game console that was released by nintendo on november 18, 2012, and is the successor of the wii.

Ex Output:
wii u


Ex Input:
a hospital ship is a big boat which is built to cure patients.

Ex Output:
hospital ship


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

Ex Output:

metis