hdu 5879 Cure 2016ACM/ICPC青岛赛区网络赛1002

Problem Description

Given an integer n, we only want to know the sum of 1/k2 where k from 1 to n.

 

Input

There are multiple cases.
For each test case, there is a single line, containing a single positive integer n. 
The input file is at most 1M.

 

Output

The required sum, rounded to the fifth digits after the decimal point.

 

Sample Input

124815

 

Sample Output

1.000001.250001.423611.527421.58044

小数据暴力一下，k->inf的时候数列之和收敛π^2/6【当时是敲了个暴力然后把1000w以上的直接用1000w输出了】