{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE BangPatterns #-}

import Control.Applicative
import Control.Monad
import Control.Arrow
import Data.List
import Data.Maybe
import Data.Char
import Text.Printf

readInt = ( readLn :: IO Int )
getInts = map ( read :: String -> Int ) . words <$> getLine

which a b f = if f then a else b
mp [ a, b ] = ( a, b )

main = do
	d <- readInt
	print $ maximum $ do
		h <- [ 0 .. d ]
		guard $ d - h * 2 >= 0
		let
			w = ( d - ( h * 2 ) ) `div` 2
		return $ h * w