Tojo hates probabilities

Problem description As a holiday gift, Tojo received a probability problem. The problem read as follows Consider an N by M grid. Rows are numbered 1 to N, from top to bottom. Columns are numbered 1 to M, from left to right. You are initially at cell (1, 1) and want to go to cell (N, M). From any cell you can move to the cell below it or to the cell right to it. You should never go out of the gri