((1 2 . 1) (2 3 . 2) (3 4 . 3) (4 5 . 4) (5 6 . 5) (6 7 . 6) (7 8 . 7) (8 9 . 8)
(9 10 . 9) (10 11 . 10) (11 12 . 11) (12 13 . 12) (13 14 . 13) (14 15 . 14)
(15 16 . 15) (16 17 . 16) (17 18 . 17) (18 19 . 18) (18 20 . 19)) &