## https://yukicoder.me/problems/no/2645

import math

MAX_ = 2 * 10 ** 7

def cum_func(cum_array, n):
    if n <= MAX_:
        return cum_array[n]
    else:
        return math.log(n) - math.log(MAX_) + cum_array[MAX_]


def main():
    N = int(input())

    cum_array = [0] * (MAX_ + 1)
    a = 0
    for i in range(1, MAX_ + 1):
        a += 1 / i
        cum_array[i] = a
    
    sqrt_n = int(math.sqrt(N))
    answer = 0
    # 約数がsqrt_n以下のもの
    for n in range(1, sqrt_n + 1):
        q = N // n
        answer += cum_func(cum_array, q) / n

    # 該当する数が約数として持つ数のわ
    for num in range(1, sqrt_n + 1):
        max_n = N // (num)
        min_n = max(N // (num + 1), sqrt_n)

        answer += (cum_func(cum_array, max_n) - cum_func(cum_array, min_n)) * cum_func(cum_array, num)

    print(answer)







        






if __name__ == "__main__":
    main()