===== Prelude 1 to Backtracking -- Queens ======

For this prelude, you are to use your skeleton file for doing backtracking and the number of solutions to the N-Queens problem.

In this variant of the 8-queens problem, you are to put N queens on an NxN chessboard, such that no two o ft

===== Input =====

Input consists of a sequence of non-negative integers, N (0 < N < 15), one per line.  

===== Output =====

For each input value, N, output the number of valid solutions to the N-Queens problem.

===== Sample Input =====

<code>
2
4
8
</code>

===== Sample Output =====

<code>
0
2
92
</code>