N = int(input())
fact = [1]

for i in range(1, N+1):
    fact.append(fact[-1]*i)

ans = 0

for x in range(2, N+1):
    ans += 2/x
    
    for y in range(1, x):
        for z in range(y+1, x):
            prob = (x-2)*fact[x-3]/fact[x]
            ans += 2*prob*y*z

ans += 1
print(ans)