INF = 10 ** 9
import sys
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)
from  collections import deque

def main():
    n = int(input())
    if n == 1:
        print(0)
        return
    
    ans = 0
    q = deque(range(2,n + 1))
    a = deque([1])
    flag = True
    cnt = 0
    while q:
        if flag:
            p = q.pop()
            if cnt == 0:
                ans += p * a[0]
                a.appendleft(p)
            else:
                ans += p * a[-1]
                a.append(p)
            cnt += 1
            if cnt == 2:
                cnt = 0
                flag = False
        
        else:
            p = q.popleft()
            if cnt == 0:
                ans += p * a[0]
                a.appendleft(p)
            else:
                ans += p * a[-1]
                a.append(p)
            cnt += 1
            if cnt == 2:
                cnt = 0
                flag = True
    ans += a[0] * a[-1]
    print(ans)

if __name__ == '__main__':
    main()