import sys

sys.setrecursionlimit(10 ** 7)
input = sys.stdin.readline
f_inf = float('inf')
mod = 10 ** 9 + 7


def resolve():
    k = int(input())
    res = 0
    for i in range(1, 10 ** 7):
        res += 1 / (i * (i + k))
    print(res)


if __name__ == '__main__':
    resolve()