Chess puzzle (Advantage)
Opening: Russian_Game, Russian_Game_Three_Knights_Game
Moves: 1. e4 e5 2. Nf3 Nf6 3. Nc3 d6 4. d3 Be7 5. h3 O-O 6. Be3 h6 7. Qd2 c5 8. O-O-O
Nc6 9. Nd5 b5 10. Nh2 Nxd5 11. exd5 Nd4 12. f4 exf4 13. Bxd4 cxd4 14. Nf3 Bf6
15. Qxf4 Re8 16. Kb1 Bb7 17. Nxd4 Be5 18. Qf2 Bxd5 19. Nxb5 *
Position (FEN): r2qr1k1/p4pp1/3p3p/1N1bb3/8/3P3P/PPP2QP1/1K1R1B1R b - - 0 19
Black to move.
Themes:  Middlegame  
Puzzle rating: 2110
Best move: a6