I got AC with a wrong solution during the contest, so I think the test cases might be a bit weak. One example my wrong solution didn't pass is:
7 63713822
It printed 3, while the best answer is 2: 7 -> 8 -> 31856912 -> 31856911 -> 63713822.

Can you please add it to the test-set?

(Edit: I've fixed my solution now, but others may fail.)

Edited by author 03.12.2016 18:42