||Problem Summary||

Given the dimensions of a rectangular grid, output a ||knight's tour|| for the grid.

||Introduction||

A ||knight's move||, given that the knight is at coordinates (x,y) is any of the following:
   (x+2,y+1) (x+1,y+2)
   (x+2,y-1) (x+1,y-2)
   (x-2,y+1) (x-1,y+2)
   (x-2,y-1) (x-1,y-2)
Given that the chosen move is a valid position on the grid.

A ||knight's tour|| is a sequence of ||knight's moves|| that visits each square of a rectangular grid.  The smallest grid for which there exists a knight's tour is 3x4.  There is no knight's tour for a 4x4 grid.

||Input|| 

Input consists of two integers seperated by a space.  The numbers correspond to the number of rows //r// and the number of columns //c// of the rectangular grid.  E.g. a grid with //r//=4 and //c//=5:

    4 5

It is guaranteed that //r// and //c// will be less than or equal to 6.  

Positions on the board are numbered left-to-right, top-to-bottom starting at zero.  (i.e. //c// * //y// + //x//)

e.g. a //r//=4 //c//=5 grid:

    0  1  2  3  4
    5  6  7  8  9
   10 11 12 13 14
   15 16 17 18 19

||Ouput|| 

Output consists of a whitespace delimited sequence of knight's moves corresponding to the positions on the board (as outlined above).  If a sequence cannot be found, the string starting with "Failed" should be output.

e.g. for a //r//=4 //c//=5 grid :

    0 7 4 13 16 5 2 9 18 11 8 1 10 17 14 3 6 15 12 19

||Scoring||

* deals with < 3x4 grids correctly
* produces correct output for all valid grids
* produces correct output for all failure grids
* (bonus) fastest
* (bonus) smallest