fun readStr () =
    let
        fun scan reader stream = SOME (StringCvt.splitl (not o Char.isSpace) reader (StringCvt.skipWS reader stream))
    in
        valOf (TextIO.scanStream scan TextIO.stdIn)
    end


val () =
    let
        val s = readStr ()

        val ans =
            if (String.size s) mod 2 <> 0 then "NO"
            else if String.substring (s, 0, (String.size s) div 2 - 1) ^ String.substring (s, 0, (String.size s) div 2 - 1) = s then "YES"
            else "NO"
    in
        print (ans ^ "\n")  
    end