N = int(input())
ans = 2
now = 0
fact = [1] * (N + 1)
for i in range(1, N + 1):
    fact[i] = fact[i - 1] * i

for i in range(3, N + 1):
    now += (i - 1)**2 * (i - 2)//2
    ans += (2 * fact[i - 1] + 2 * now * (i - 2) * fact[i - 3])/fact[i]

print(ans)