White to Play
Published in Chess Puzzles

Time to mate the black king. How much time will you need?
This game between Gubanow and Urajew in St. Petersburg in the early 20th century ended this way: 1.Qxg7+ Bxg7 2.Rf7+ Kd6 3.Nb5+ Kd5 4.c4+ Ke4 5.Re1#