import math

N = int(input())

def zeta(x):
    return 1/x

zeta_c = [0] * (10**6 + 1)
for i in range(1,10**6 + 1):
    zeta_c[i] = zeta_c[i-1] + 1/i
def zeta_cumsum(x):
    if x <= 10**6:
        return zeta_c[x]
    else:
        return math.log(x) + 0.5772156649

M = int(N ** 0.5)

ans = 0
for i in range(1, M+1):
    ans += zeta_cumsum(N//i) * zeta(i)

for j in range(1, M+1):
    ans += (zeta_cumsum(N//j) - zeta_cumsum(M))* zeta(j)

print(ans)