from collections import *

N = int(input())
if N == 1:
    print(0)
    exit()
ans = 0
L = deque(range(1, N + 1))
D = deque()
D.append(L.popleft())
cnt = 0
while len(L) >= 2:
    if cnt % 2:
        v = L.popleft()
        ans += D[-1] * v
        D.append(v)
        v = L.popleft()
        ans += D[0] * v
        D.appendleft(v)
    else:
        v = L.pop()
        ans += D[-1] * v
        D.append(v)
        v = L.pop()
        ans += D[0] * v
        D.appendleft(v)
    cnt += 1
if L:
    ans += D[-1] * L[0]
    ans += D[0] * L[0]
else:
    ans += D[0] * D[-1]
print(ans)