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:
tronchoy is a commune.

Ex Output:
tronchoy


Ex Input:
ernest gary gygax (july 27, 1938 – march 4, 2008) (ipa: ˈgaj.gæks) was an american writer and game designer.

Ex Output:
gary gygax


Ex Input:
the actinide series is the 15 chemical elements between actinium and lawrencium on the periodic table.

Ex Output:

actinide