Problem 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.

1
2
4
8
15

1.00000
1.25000
1.42361
1.52742
1.58044