fun member x nil = false
  | member x (h::tl) =
    if x = h
    then true
    else member x tl


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



fun findAns s =
    let 
        fun findAnsAux [] acc = findAnsAux acc []
          | findAnsAux ((toTaken, toAdd)::tl) acc = 
            case List.length toTaken = 0 of
                true => List.map (fn (_, allAdded) =>
                                     String.implode (List.rev allAdded))
                                 ((toTaken, toAdd)::tl)
              | false => 
                let
                    val first = List.hd toTaken
                    val firstRemoved = List.tl toTaken
                    val last = List.last toTaken
                    val lastRemoved = List.rev (List.tl (List.rev toTaken))
                in
                    findAnsAux tl ((firstRemoved, first :: toAdd) :: (lastRemoved, last :: toAdd) :: acc)
                end
    in
        List.length
            (
              List.foldl (fn (x, acc) =>
                             if member x acc then acc
                             else x :: acc)
                         []
                         (findAnsAux [(String.explode s, [])] [])
            )
    end


val () =
    let
        val s = readStr ()

        val ans = findAns s
    in
        print (Int.toString ans ^ "\n")
    end