What is the number on?
The number is on the sign.
    src        edge_attr  dst
0     0               on    1
1     0   to the left of    1
2     1  to the right of   12
3     1  to the right of    0
4     1  to the right of    2
5     1  to the right of    4
6     1  to the right of    9
7     2  to the right of    6
8     2   to the left of    1
9     2  to the right of   10
10    3   to the left of    8
11    3   to the left of    4
12    3   to the left of    9
13    4   to the left of    7
14    4   to the left of    1
15    4  to the right of    3
16    4  to the right of    6
17    6   to the left of    4
18    6   to the left of    9
19    6   to the left of    2
20    6   to the left of    8
21    7  to the right of    9
22    7               on    1
23    7  to the right of    4
24    8  to the right of    3
25    8  to the right of    6
26    8  to the right of   11
27    8               on    5
28    9   to the left of    7
29    9  to the right of    3
30    9   to the left of    1
31    9  to the right of   11
32    9  to the right of    6
33    9  to the right of   10
34   10   to the left of    9
35   10   to the left of    2
36   11   to the left of    9
37   11   to the left of    8
38   12               on    0
39   12   to the left of    1