9 0 7 6 5 4 3 2 1
9
a 1 1
b 2 2
c 3 3
d 4 4
e 5 5
f 1 2
f c
f 4
f f
f 5
a b
a a
a c
a a
a d
a a
a e
a f
a a
a 7
6 a
6 6
0 7 6 5 4 3 2 1
9 0 7 6 5 4 3 2 1
9