from collections import defaultdict

def make_divisors(n):
    divisors = []
    i = 1
    while i ** 2 <= n:
        if n % i == 0:
            divisors.append(i)
            if i ** 2 != n:
                divisors.append(n // i)
        i += 1
    divisors.sort()
    return divisors

def f(x):
    if x == 1:
        return 0
    P = (x / (x - 1)) ** 2
    D = make_divisors(x)
    dic = defaultdict(int)

    S = set()
    for d in reversed(D[1:]):
        i = 1
        while i * d <= N:
            if i * d not in S:
                S.add(i * d)
                dic[d] += 1
            i += 1
    dic[1] = N - sum(dic.values())
    ret = 0
    for d in D[:-1]:
        ret += f(d) / x * dic[d]
    return (ret + 1) * x / (x - 1)

N = int(input())
print(f(N))