wotax :: Int -> Maybe Int
wotax n = let x = div ((n + 1) * 100) 108 in
          if div (x * 108) 100 == n then Just x
          else Nothing

myShow Nothing = ":("
myShow (Just x) = show x

main = do
  n <- readLn :: IO Int
  putStrLn $ myShow $ wotax n
