r1b1q2r/p1p2p1p/n2nk2b/1p1pp3/P2P2PP/NPN1P3/RBPQ2P1/4KB1R b K - 4 20
FEN state: r1b1q2r/p1p2p1p/n2nk2b/1p1pp3/P2P2PP/NPN1P3/RBPQ2P1/4KB1R b K - 4 20 ; Best move: b5b4
The current state of the chess board is: Black rook at a8, black bishop at c8, black queen at e8 and black rook at h8. Black pawn at a7, black pawn at c7, black pawn at f7 and black pawn at h7. Black knight at a6, black knight at d6, black king at e6 and black bishop at h6. Black pawn at b5, black pawn at d5 and black pawn at e5. White pawn at a4, white pawn at d4, white pawn at g4 and white pawn at h4. White knight at a3, white pawn at b3, white knight at c3 and white pawn at e3. White rook at a2, white bishop at b2, white pawn at c2, white queen at d2 and white pawn at g2. White king at e1, white bishop at f1 and white rook at h1. White kingside is the only castle move available. Half move number is 4. Full move number is 20. Black to move.