> [[[1, 6, 2, 10]]]
> [[1, 6, 2, 10]]
> [1, 6, 2, 10]
< [1, 6, 2, 10]
< [[1, 6, 2, 10]]
< [[1, 6, 2, 10]]
< [[1, 6, 2, 10]]
8