#!/usr/bin/env python3

import fractions


def inv(x):
    return fractions.Fraction(1, x)


# http://www.cis.nagasaki-u.ac.jp/~masada/Digamma2010042801.pdf
def trigamma(x):
    ans = inv(x)
    ans += inv(2 * x ** 2)
    ans += inv(6 * x ** 3)
    ans -= inv(30 * x ** 5)
    ans += inv(43 * x ** 7)
    ans -= inv(30 * x ** 9)
    ans += 5 * inv(66 * x ** 11)
    ans -= 691 * inv(2730 * x ** 13)
    ans += 7 * inv(6 * x ** 15)
    return ans


def main():
    x = fractions.Fraction(input())
    if x == 0:
        res = 1.6449340668482426
    else:
        res = trigamma(x + 1)
    print("{:.16f}".format(float(res)))


if __name__ == '__main__':
    main()