Partition of a directed bipartite graph into two directed cycles

Let D = (V-1, V-2; A) be a directed bipartite graph with \V-1\ = \V-2\ = n greater than or equal to 2. Suppose that d(D)(x) + d(D)(y) greater than or equal to 3n + 1 for all x is an element of V-1 and y is an element of V-2. Then D contains two vertex-disjoint directed cycles of lengths 2n(1) and 2n(2), respectively, for any positive integer partition n = n(1) + n(2). Moreover, the condition is sharp for even n and nearly sharp for odd n.