Can you help me ?

Now for something completely different.

Though I'm usually no big fan of chess variants and unorthodox problems, I can't resist sharing the very entertaining and puzzling problem a chess friend has shown us at the club today.

Normal chess rules apply, but from the initial position, white has agreed to play 1.f3 2.Kf2 3.Kg3 and 4.Kh4 in this order, no matter what.

The problem is : how can black checkmate him on the 4th move (ie. after 4.Kh4) ?