Not terribly difficult. The only correct first move is the natural one- 1.Kb2. White has to ensure that his king can reach d4 as soon as the black king can get to f5 should black try 1...Kg6 and 2......Kf5. With 1.Kb2, black must then try to get around to the other side to cut white off, but this met pretty easily by multiple ways- white just must not dilly dally in keeping the black king out of d5.