Task about path in matrix

You have matrix M N.

You need to find the longest path in a matrix when you start in [0][0] and going to [m-1][n-1]. In the way you have labels that signed "1" another cells are "0". If you meet "1" you should increase path on 1. User is entering M, N and cells that "1"; In your moving you can move only right or down. Output this path.