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: spintronics is a kind of electronics that uses the tiny magnetic fields that come from electrons as well as their electric charge.
Example Output: spintronics

Example Input: the vektor r4 is a south african assault rifle.
Example Output: vektor r4

Example Input: troy smith (born july 20, 1984 in cleveland, ohio) is an american football quarterback that most recently played for the omaha nighthawks of the united football league.
Example Output:
troy smith