Disjoint cycles in directed graphs

Let s and t be two non-negative integers and let D be a directed graph of order n >= 3s + 4t + 3. In this paper we will show that if the minimum sum of in-degree and out-degree delta(D) >= (3n - 3)/2, then D contains s +t + 1 disjoint cycles C-1, ... , Cs+t+1 such that vertical bar CS vertical bar = 3 for each i with 1 <= i <= s, vertical bar C-i vertical bar = 4 for each i with s + 1 <= i <= s + t and vertical bar Cs+t+1 vertical bar = n - 3s - 4t. Furthermore, the degree condition is sharp.