What is the fence made of?
The fence is made of metal.
    src        edge_attr  dst
0     0   to the left of    7
1     1   to the left of   17
2     1  to the right of   13
3     3   to the left of    4
4     3   to the left of   17
5     3  to the right of    5
6     3   to the left of    6
7     4   to the left of    9
8     4  to the right of    6
9     4   to the left of   17
10    4  to the right of    3
11    5   to the left of    3
12    5   to the left of    7
13    6   to the left of   17
14    6  to the right of    7
15    6   to the left of    4
16    6  to the right of    3
17    6   to the left of    9
18    7  to the right of    0
19    7  to the right of    5
20    7   to the left of    6
21    7   to the left of   15
22    9  to the right of    4
23    9  to the right of    6
24    9  to the right of   15
25    9  to the right of   10
26    9               on   17
27   10   to the left of    9
28   11  to the right of   18
29   11  to the right of   12
30   12  to the right of   16
31   12   to the left of   11
32   13   to the left of    1
33   14   to the left of   17
34   15   to the left of   17
35   15   to the left of    9
36   15  to the right of    7
37   16   to the left of   12
38   17  to the right of    1
39   17  to the right of    3
40   17  to the right of   15
41   17  to the right of    4
42   17  to the right of    6
43   17  to the right of   14
44   18   to the left of   11