15 20
0 1
0 14
1 2
1 13
2 3
2 12
3 4
3 11
4 5
4 10
5 6
5 9
6 8
7 8
8 9
9 10
10 11
11 12
12 13
13 14

0--1--2--3--4--5-6
|  |  |  |  |  | |
14-13-12-11-10-9-8-7
