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: "polythene pam" is a song written by john lennon, credited to lennon/mccartney, and performed by the beatles on their album "abbey road".
Example Output: polythene pam

Example Input: patau syndrome affects about one in 25,000 live births.
Example Output: patau syndrome

Example Input: goguryeo is a dynasty of ancient korea which was begun by jumong in 37 bc.
Example Output:
goguryeo