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:
mariner 10 was a robotic nasa space probe.

Ex Output:
mariner 10


Ex 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.

Ex Output:
troy smith


Ex Input:
an ectopic pregnancy is a when an embryo implants itself (sticks to somewhere) outside the uterus.

Ex Output:

ectopic pregnancy