import math
mx = 1000000

logmx = math.log(mx)
H_table = [0] * (mx+1)

def H(n):
	if n < 0: return 0.0
	if n <= mx: return H_table[n]
	return H_table[mx] + math.log(n) - logmx

for i in range(1, mx+1):
	H_table[i] = H_table[i-1] + 1 / i

n = int(input())
ans = 0.0
i = n
while i > 0:
	v = n // i
	j = n // (v + 1)
	ans += H(v) * (H(i) - H(j))
	i = j

print(ans)