Sum of a Fibonacci-like Fraction Sequence

Problem Description

Compute the sum of the first $N$ terms of the sequence $2/1 + 3/2 + 5/3 + 8/5 + \dots$. Note that starting from the second term, the numerator of each term equals the sum of the previous term's numerator and denominator, and the denominator equals the previous term's numerator.

Input Format

A single positive integer $N$ given on one line.

Output Format

Output the value of the partial sum on one line, accurate to two decimal places. The result is guaranteed not to exceed the range of double precision.

Sample Input

20

Sample Output

32.66

Constraints

$1 \le N \le 10^4$