super easy mate is 4

I was thinking in the direction of 1.Bxb7 Ka7 2.Rb1 Kb8 3.Bc6 Ka7 4. Nc4+ Qa5. 5.Rxa5#
The last move of the queen can be located anywhere in my solution, but the white rooks can always take the queen. Instead of moving the king then, black moves the queen.