n = int(input())
if n == 1:
    print(0)
    exit()
A = list(range(1, n + 1))
for i in range(1, n // 2, 2):
    A[i], A[n - i - 1] = A[n - i - 1], A[i]
ans = 0
for i in range(n):
    ans += A[i - 1] * A[i]
print(ans)