k = int(input())

t = [0] * 1048576
for n in range(1, 1048576 + 1):
    t[n - 1] = 1 / (n * (n + k))

x = 1
while x < 1048576:
    for i in range(0, 1048576, x * 2):
        t[i] += t[i + x]
    x *= 2

print(t[0])