There are ***30 candidates in the entrance examination room, arranged in four columns. That is, the arrangement of seven seven eight eight. The front door of the examination room is arranged in a serpentine shape from the back.
7 8 22 23
6 9 2 1 24
5 10 20 25
4 1 1 19 26
3 12 18 27
2 13 17 28
1 14 16 29
15 30