Clarification needed in Chef and strange matrix (chefbm)

please clarify

As per constraints 1 ≤ n, m. if n is 1 only one column. how cost can be calculated through a(i)(j) - a(i)(j - 1).

As the cost of a movement is a(i)(j) - a(i)(j - 1).

I am getting wrong answer even if my output is exactly matched.