import Control.Monad.ST
import Data.STRef
import Control.Monad

main :: IO ()
main = do
  s <- getLine
  putStrLn $ oddString s

oddString s = runST $ do
  str <- newSTRef ""
  forM_ [0..length s - 1] $ \i ->
    if i `mod` 2 == 1
      then return ()
      else
        modifySTRef str (++ [s !! i])

  readSTRef str
