import Control.Applicative
import Data.List
import Data.Ord
import Data.Char

sieve' = 2:3:[x|i<-[1..],j<-[-1,1], let x = 6*i+j, isPrime x] where
  isPrime n = null [p|p<-takeWhile (\x -> x*x <=n) sieve', rem n p == 0]

solve :: [Int] -> Int
solve ns = fst $ head $ iter' $ zip ns $ fmap hash ns where
    hash x = let x' = sum . fmap digitToInt . show $ x in
        if length (show x') == 1 then x'
        else hash x'
    
    iter' xs = maximumBy (comparing (\xs -> (length xs, fst $ head xs))) [flip iter [] $ drop p xs|p<-[0..length xs]]

    iter [] acc = acc
    iter (x:xs) acc = if snd x `elem` fmap snd acc then acc else iter xs (x:acc)
    
main = do
    k <- (read :: String -> Int) <$> getLine
    n <- (read :: String -> Int) <$> getLine
    print $ solve $ reverse $ dropWhile (<k) $ takeWhile (<=n) $ sieve'