NxM
  |      b             a
--+-------------------------
  | 1    4    5   -1   9   ...
  | 0    3    0   17  -3   ...
b>| 1   10    3    0   3   ...
  |-8   -3    2    1  -4   ...
a>| 0    8    4    0   0
...

##</code><code>##

My starting position is (a,a) = 0
My end position is  (b,b) = 10

##</code><code>##

pathA: left, up, left, left, up =  0+0+1+2+(-3)+10 = 10
pathB: left-slide + up-slide = 0+8+10 = 18   
pathC: up-slide + left + up + left-slide+down = 0+3+0+17+3+10= 33

etc..