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:
heybeliada is an island in sea of marmara in turkey.

Ex Output:
heybeliada


Ex Input:
parnassiinae is a subfamily of butterflies.

Ex Output:
parnassiinae


Ex Input:
metal gear is an action-adventure stealth video game franchise made by konami.

Ex Output:

metal gear


