import math

def trigamma(x):
    if x >= 10:
        return trigamma_asymptotic(x)
    else:
        m = max(0, math.ceil(10 - x))
        sum_part = sum(1.0 / (x + k)**2 for k in range(m))
        return sum_part + trigamma(x + m)

def trigamma_asymptotic(x):
    result = 1.0 / x
    result += 1.0 / (2 * x**2)
    result += 1.0 / (6 * x**3)
    # Terms from Bernoulli numbers up to B_20
    terms = [
        (-1/30, 5),      # B_4 term: -1/(30*2x^5) → -1/(60x^5)
        (1/42, 7),       # B_6 term: 1/(42*3x^7) → 1/(126x^7)
        (-1/30, 9),      # B_8 term: -1/(30*4x^9) → -1/(120x^9)
        (5/66, 11),      # B_10 term:5/(66*5x^11) → 1/(66x^11)
        (-691/2730, 13), # B_12 term: -691/(2730*6x^13)
        (7/6, 15),       # B_14 term:7/(6*7x^15) →1/(6x^15)
        (-3617/510, 17), # B_16 term:-3617/(510*8x^17)
        (43867/798, 19), # B_18 term:43867/(798*9x^19)
        (-174611/330, 21)# B_20 term:-174611/(330*10x^21)
    ]
    for B, exponent in terms:
        term = B / (x ** exponent)
        result += term
        if abs(term) < 1e-20:
            break
    return result

x = float(input().strip())
if x == 0:
    print("{0:.15f}".format(math.pi**2 / 6))
else:
    s = x + 1.0
    result = trigamma(s)
    print("{0:.15f}".format(result))