from collections import deque
N=int(input())
if N==1:
    ans=0
else:
    queue=deque([x for x in range(2,N+1)])
    L=[1]
    R=[1]
    b=1
    while queue:
        if len(queue)==1:
            L.append(queue.pop())
            break
        if b:
            R.append(queue.pop())
            L.append(queue.pop())
        else:
            R.append(queue.popleft())
            L.append(queue.popleft())
        b^=1
    tour=L+R[::-1]
    ans=sum(a*b for a,b in zip(tour,tour[1:]))
print(ans)