import sys

sys.setrecursionlimit(10 ** 6)
stdin = sys.stdin

ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline().strip()
nsa = lambda: list(stdin.readline().split())
mod = 10 * 7 + 7

n = ni()
ans = 0

for i in range(3, n + 1, 2):
    ans += (n - i) + 1

print(ans)