import math

N = int(input())
fact = [math.factorial(x) for x in range(N + 1)]
ans = 2

for num in range(3, N + 1):
    ans += 2.0 / num
    for at in range(1, num - 1):
        for a in range(1, num):
            for b in range(a + 1, num):
                ans += 2 * a * b * fact[num - 3] / fact[num - 1] / num

print(ans)