What is the railroad made of?
The railroad is made of metal.
    src        edge_attr  dst
0     1  to the right of    2
1     1           beside   14
2     2   to the left of    1
3     3   to the left of   14
4     3  to the right of    6
5     4   to the left of   14
6     4  to the right of    7
7     4  to the right of    6
8     4  to the right of   13
9     4   to the left of    8
10    5               on    1
11    5            below    9
12    5   to the left of    8
13    5  to the right of   13
14    5  to the right of   10
15    5   to the left of   14
16    6  to the right of   10
17    6  to the right of   13
18    6   to the left of    4
19    6   to the left of    3
20    6  to the right of    7
21    7   to the left of    4
22    7   to the left of    6
23    8  to the right of    4
24    8  to the right of    5
25    9            above    5
26   10   to the left of    6
27   10   to the left of    5
28   13   to the left of    5
29   13   to the left of    6
30   13   to the left of    4
31   14  to the right of    5
32   14  to the right of    3
33   14  to the right of    4