You can also refer to locations such as (4, 0) or (-4, 3), which are
both the same as (0, 0) in a 4x3 ocean. (More generally, the coordinates in
an ixj ocean are taken modulo i for the x-coordinate, which is horizontal, and
modulo j for the y-coordinate, which is vertical.) Any pair of integers will
give you a valid position in the grid by "wrapping around" at the edges.