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 Q]: "hail to the chief" is the official presidential anthem of the united states.
[EX A]: hail to the chief

[EX Q]: an electronic book (also called an e-book, ebook or digital book) is a book in digital form.
[EX A]: e-book

[EX Q]: anton rubinstein (born vikhvatinets 28 november 1829; died petershof 20 november 1894) was a russian pianist and composer.
[EX A]:
anton rubinstein