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