Alternating Harmonic Series

Calculate the alternating harmonic series defined by the formula: \( S_n = \frac{1}{1} - \frac{1}{2} + \frac{1}{3} - \frac{1}{4} + \cdots + (-1)^{n-1}\times\frac{1}{n} \).

Given an integer n, compute S_n.

inputFormat

An integer n is given on a single line. (For example: 1 ≤ n ≤ 10⁶)

outputFormat

Output the computed value of S_n rounded to 6 decimal places.

sample

1

1.000000