https://codeforces.com/blog/entry/56422?#comment-401173 http://www.eecs.harvard.edu/~htk/publication/1978-jacm-brent-kung.pdf
https://codeforces.com/blog/entry/56422?#comment-401173
http://www.eecs.harvard.edu/~htk/publication/1978-jacm-brent-kung.pdf