Discussion @ 1252. Sorting the Tombstones @ Timus Online Judge

BYF Why we should use GCD in this problem? [1] // Problem 1252. Sorting the Tombstones 29 Oct 2004 19:30

I've got AC, but I don't know the reason exactly.
I just guessed it, and got AC.

BYF Re: Why we should use GCD in this problem? // Problem 1252. Sorting the Tombstones 30 Oct 2004 13:55

How about this case?
5
2 1 3 4 5
I think k could be 2
2 5 3 4 1
1 5 3 4 2
1 2 3 4 5
But my program output 0
Do I misunderstand this problem or something else?

Discussion of Problem 1252. Sorting the Tombstones