import qualified Data.Set as S

eratosthenes n = f [] [2..n] where
    f pn ys | pn /= [] && (head pn)^2 > n   = (reverse pn) ++ ys
            | otherwise                     = f ((head ys):pn) (filter (p (head ys)) ys)
    p m z = z `mod` m /= 0


solve' n = head (S.toList (S.difference (S.fromList [m..n]) (S.fromList pn))) where
    m   | n - 100 < 2   = 2
        | otherwise     = n - 100
    pn = filter p (eratosthenes n)
    p x = x >= n - 100 && x <= n + 100

main = readLn >>= print . solve'