#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import itertools
import math


def compute_expectation(n):
    fact = math.factorial
    ans = 1.0
    for i in range(2, n + 1):
        ans += 2.0 / i
        if i > 2:
            for c1, c2 in itertools.combinations(range(1, i), 2):
                ans += c1 * c2 * fact(i - 2) * 2.0 / fact(i - 1) / i
    return ans


def main():
    print("{:.12f}".format(compute_expectation(int(input()))))


if __name__ == '__main__':
    main()