Maximal Total Length Of k Disjoint Cycles In Bipartite Graphs

Let k, s and n be three integers with s≥k≥2, n≥2k+1. Let G=(V1,V2;E) be a bipartite graph with |V1|=|V2|=n. If the minimum degree of G is at least s+1, then G contains k vertex-disjoint cycles covering at least min(2n,4s) vertices of G.