CF87C Interesting Game

Two best friends Serozha and Gena play a game. Initially there is one pile consisting of $ n $ stones on the table. During one move one pile should be taken and divided into an arbitrary number of piles consisting of $ a_{1}>a_{2}>...>a_{k}>0 $ stones. The piles should meet the condition $ a_{1}-a_{2}=a_{2}-a_{3}=...=a_{k-1}-a_{k}=1 $ . Naturally, the number of piles $ k $ should be no less than two. The friends play in turns. The player who cannot make a move loses. Serozha makes the first move. Who will win if both players play in the optimal way?

The single line contains a single integer $ n $ ( $ 1

If Serozha wins, print $ k $ , which represents the minimal number of piles into which he can split the initial one during the first move in order to win the game. If Gena wins, print "-1" (without the quotes).