# -*- coding: utf-8 -*-

D, = map(int, raw_input().split())

if D < 4:
    print 0
    exit()

maxs = 0
for w in xrange(1, D/2):
    # 幅wセンチの時の面積
    h = int((D - 2 * w) / 2)
    if h < 1: continue
    s = w * h
    maxs = max(maxs, s)

print maxs