Number of Ways

Devu is learning Combinatorics in his college. He find it very interesting to calculate number of ways of going to point (c,d) from point (a,b) in co-ordinate plane. We can take horizontal and vertical steps only and can not visit at a point twice. In a step, you can move one unit only. We have to reach to the point (c,d) from the point (a,b) using abs(a-c)+ abs(b-d) steps only. Devu has two se