def chmax(a, b):
    if a < b:
        a = b
        return True
    return False

def chmin(a, b):
    if b < a:
        a = b
        return True
    return False

INTINF = 1000001000
INTMAX = 2147483647
LLMAX = 9223372036854775807
LLINF = 1000000000000000000

def main():
    N = int(input())
    memo = {}

    memo[1] = 0.0

    def solve(n):
        if n in memo:
            return memo[n]

        divsum = 0
        d = 2
        while d * d <= n:
            if n % d == 0:
                divsum += solve(d)

                if d != n // d:
                    divsum += solve(n // d)
            d += 1

        ret = float(n) / float(n - 1) + divsum / float(n - 1)
        memo[n] = ret
        return ret

    print(f"{solve(N):.10f}")

if __name__ == "__main__":
    main()