# Introduction

You have stumbled upon a group of mathematicians who are also singer-songwriters.
They have written a song for each of their favorite numbers, and, as you can imagine, they have a lot of favorite numbers (like [0][zero] or [73][seventy-three] or [6174][kaprekars-constant]).

You are curious to hear the song for your favorite number, but with so many songs to wade through, finding the right song could take a while.
Fortunately, they have organized their songs in a playlist sorted by the title — which is simply the number that the song is about.

You realize that you can use a binary search algorithm to quickly find a song given the title.

[zero]: https://en.wikipedia.org/wiki/0
[seventy-three]: https://en.wikipedia.org/wiki/73_(number)
[kaprekars-constant]: https://en.wikipedia.org/wiki/6174_(number)
