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.

Input: Consider Input: ronald ross (13 may 1857 16 september 1932) was an english doctor.

Output: ronald ross

Input: Consider Input: lyme regis is a coastal town in west dorset, england, 25 miles west of dorchester and 25 mi east of exeter.

Output: lyme regis

Input: Consider Input: the grecopersian wars were a series of wars fought between classical greece and persia's achaemenid empire in the 5th century bc.
Output: grecopersian wars