import Control.Monad.ST
import Control.Monad
import Data.Array.ST
import Data.Array
import Data.STRef
import Control.Monad
import Control.Applicative
import Data.List
primes ::[Integer]
primes = 2:f [3] [3,5..]
         where f (x:xs) ys = let (ps,qs) = span (<x^2) ys
                             in ps ++ f (xs ++ ps) [z | z<-qs,mod z x /= 0]

main = do
  [l,h] <- map read <$> words <$> getLine ::IO [Integer]
  let p = reverse $ (1:(takeWhile (<=100000) primes))
  print $ head [h-(mod h i)| i<-p,l<=h-(mod h i),i<=div (h-(mod h i)) i]