import Data.Array.Unboxed

primesSA :: [Int]
primesSA = 2 : oddprimes ()
  where 
    oddprimes () = 3 : sieve (oddprimes ()) 3 []
    sieve (p:ps) x fs = [i*2 + x | (i,True) <- assocs a] 
                        ++ sieve ps (p*p) ((p,0) : 
                             [(s, rem (y-q) s) | (s,y) <- fs])
     where
      q = (p*p-x)`div`2
      a :: UArray Int Bool
      a = accumArray (\ b c -> False) True (1,q-1)
                     [(i,()) | (s,y) <- fs, i <- [y+s, y+s+s..q]]
                     
main = getLine >>=   -- 2/1 mln: n^1.08 !
       (\r-> print . last . take (read r) $ primesSA)