2016 IMO Shortlist C5

Let $n \geq 3$ be a positive integer. Find the maximum number of diagonals of a regular $n$-gon one can select, so that any two of them do not intersect in the interior or they are perpendicular to each other.

令 $n \geq 3$ 为正整数。求一个可以选择的正则 $n$ 边形的最大对角线数，使得它们中的任何两条在内部不相交或彼此垂直。