What is the material of the staircase?
The staircase is made of metal.
    src        edge_attr  dst
0     0  to the right of    9
1     0  to the right of   13
2     1  to the right of    2
3     2   to the left of    1
4     2   to the left of   14
5     3   to the left of    5
6     3  to the right of    8
7     4   to the left of    5
8     5  to the right of    3
9     5  to the right of    4
10    5   to the left of   14
11    8  to the right of   12
12    8   to the left of    3
13    9   to the left of   11
14    9   to the left of    0
15   10   to the left of   14
16   11  to the right of    9
17   11  to the right of   13
18   12   to the left of    8
19   13   to the left of    0
20   13   to the left of   11
21   14  to the right of    2
22   14  to the right of    5
23   14  to the right of   10