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:
yoshihiro uchimura (born 24 august 1984) is a japanese football player.

Ex Output:
yoshihiro uchimura


Ex Input:
jeong mong-ju (, hanja:鄭夢周, 1337 - april 1392) was a korean goryo dynasty politician, writer, poet and thinker.

Ex Output:
jeong mong-ju


Ex Input:
approximation theory is a field of mathematics which is concerned with approximating the values of a function.

Ex Output:

approximation theory