from heapq import heappop, heappush

k = int(input())

t = []
for n in range(1, 100000):
    heappush(t, 1 / (n * (n + k)))

while len(t) != 1:
    a = heappop(t)
    b = heappop(t)
    heappush(t, a + b)

print(t[0])