IrMO 2017 Problem 8

A line segment $B_0B_n$ is divided into $n$ equal parts at points $B_1,B_2,...,B_{n-1}$ and $A$ is a point such that $\angle B_0AB_n$ is a right angle. Prove that : $$\sum_{k=0}^{n} |AB_k|^{2} = \sum_{k=0}^{n} |B_0B_k|^2$$