9 4 2 a b 21 0 blank 7 blank R 0 a 1 leftend R 0 b 4 leftend R 1 blank 2 blank L 1 a 1 a R 1 b 1 b R 2 leftend 7 leftend R 2 b 8 b R 2 a 3 blank L 3 a 3 a L 3 b 3 b L 3 leftend 0 leftend R 4 a 4 a R 4 b 4 b R 4 blank 5 blank L 5 leftend 7 leftend R 5 a 8 a R 5 b 6 blank L 6 a 6 a L 6 b 6 b L 6 leftend 0 leftend R