CF380E Sereja and Dividing

Let's assume that we have a sequence of doubles $ a_{1},a_{2},...,a_{|a|} $ and a double variable $ x $ . You are allowed to perform the following two-staged operation: 1. choose an index of the sequence element $ i $ $ (1

The first line contains integer $ |b| $ $ (1

In a single line print a real number — the required sum divided by $ |b|^{2} $ . Your answer will be considered correct if its absolute or relative error won't exceed $ 10^{-6} $ .