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:
rsgc1 is a massive young open star cluster in the milky way galaxy.

Ex Output:
rsgc1


Ex Input:
colonel archibald gracie iv (january 17, 1859 – december 4, 1912) was an american writer, amateur historian, real estate investor, and survivor of the sinking of the r.m.s titanic.

Ex Output:
archibald gracie iv


Ex Input:
the battle of mine creek (also known as the battle of the osage) was a battle in the american civil war.

Ex Output:

battle of mine creek