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.

Example Input: a black powder rocket motor pushes a model rocket using black powder.
Example Output: black powder rocket motor

Example 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.
Example Output: wii u

Example Input: ionia was a region in the west of asia minor in ancient greek times.
Example Output:
ionia