I think most ACMers are familiar with grid map.
In a grid map. Each grid has its own value vij.
At the beginning you are on (0,0) and you have to go to (M,N)
You have two ways to move (0,1) and (1,0)
(0,1) means when you stand on(x,y) you move to (x,y+1)
(1,0) means when you stand on(x,y) you move to (x+1,y)
Now you have to find a way from (0,0) to (M,N) to make the combined value of all the grid you have passed is the largest.
Output the maximum combined value.