{-# LANGUAGE OverloadedStrings #-}
import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as B

main :: IO ()
main = do
    s <- B.getLine
    let k = if odd $ B.length s
                then "NO" :: ByteString
                else f s
    B.putStrLn k

f :: ByteString -> ByteString
f bs = if a == b then ("YES" :: ByteString) else ("NO"  :: ByteString)
    where
        (a, b) = B.splitAt (B.length bs `div` 2) bs