Chess puzzle (Checkmate)
Moves: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. c3 Nf6 5. d4 exd4 6. b4 Bb6 7. e5 Qe7 8. cxd4
Nxb4 9. O-O Ng8 10. Bg5 f6 11. exf6 gxf6 12. Re1 fxg5 13. Rxe7+ Nxe7 14. Nxg5
d5 15. Qh5+ Ng6 16. Nxh7 Kf7 17. Bxd5+ Nxd5 18. Qxd5+ Be6 19. Ng5+ Kf6 20. Nxe6
Rhe8 21. Nc5 *
Position (FEN): r3r3/ppp5/1b3kn1/2NQ4/3P4/8/P4PPP/RN4K1 b - - 2 21
Black to move.
Themes:  Middlegame Back Rank Mate, Mate in 1 
Puzzle rating: 523
Best move: Re1#