import Control.Applicative ((<$>))
import Data.List (find)

main :: IO ()
main = solve <$> read <$> getLine >>= print

solve :: Int -> Int
solve n = maybe (f n) id . find ((== 0) . (mod n)) . takeWhile ((<= n) . (^ 2)) $ [3 ..]
  where f x | even x = let y = x `div` 2 in if y > 2 then y else x
            | otherwise = x