import Control.Applicative

main :: IO ()
main = solve <$> readLn >>= putStrLn

solve :: Int -> String
solve n = f 0 50000
  where
    f s l
      | s + 1 == l = ":("
      | t == n = show m
      | t < n = f m l
      | t > n = f s m
      where
        m = (s + l) `div` 2
        t = tax m
        
tax :: Int -> Int
tax = (flip div 100) . (* 108)
