import math

def asymptotic_psi1(z):
    result = 1.0 / z + 1.0 / (2.0 * z ** 2)
    # 漸近展開の項をベルヌーイ数に基づいて追加
    terms = [
        (1, 6, 3),
        (-1, 30, 5),
        (1, 42, 7),
        (-1, 30, 9),
        (5, 66, 11),
        (-691, 2730, 13),
        (7, 6, 15),
        (-3617, 510, 17),
        (43867, 798, 19),
        (-174611, 330, 21),
    ]
    for numerator, denominator, exponent in terms:
        term = (numerator / denominator) / (z ** exponent)
        result += term
        # 項の絶対値が小さくなりすぎたら打ち切る
        if abs(term) < 1e-20:
            break
    return result

x = float(input())
z = x + 1.0
A = 20.0  # 閾値

if z < A:
    K = math.ceil(A - z)
    sum_terms = 0.0
    for k in range(K):
        current_z = z + k
        sum_terms += 1.0 / (current_z ** 2)
    new_z = z + K
    psizK = asymptotic_psi1(new_z)
    ans = psizK + sum_terms
else:
    ans = asymptotic_psi1(z)

# 小数点以下16桁まで表示
print("{0:.16f}".format(ans))