White play : mate in 4

I realised I have posted many 'Black to Play' positions, so for a change, here is 'White to Play": and mate in 4, courtesy of the London System and a naive opponent.

White to play

Yes, this is just a blitz game, but it was still amazing to see Black's last move of 9...f5. 

I didn't need to think much before moving, and after that, the mate just played itself.

This is a simple, and obvious, example of not thinking in the opening. Black just wanted to set up his "system" of crenellated pawns, saw a direct attack possible on the bishop , and played it. Result misery...at least eventually.

You don't need me to post the solution !