# Cure

Time Limit: 3000/1000 MS (Java/Others)

Memory Limit: 32768/32768 K (Java/Others)

## Description

Given an integer $n$, we only want to know the sum of $1/k^2$ 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

1
2
4
8
15

## Sample Output

1.00000
1.25000
1.42361
1.52742
1.58044

wange2014

## Source

2016 ACM/ICPC Asia Regional Qingdao Online