# coding: utf-8
# Your code here!
import sys
read = sys.stdin.read
readline = sys.stdin.readline

d = int(readline())//2
#*x, = map(int,readline().split())
ans = 0
for i in range(d):
    for j in range(d):
        if i+j > d: break
        ans = max(ans,i*j)
print(ans)