open System

[<EntryPoint>]
let main argv =

    let rec mem list x =
        match list with
        | [] -> false
        | head :: tail ->
            if x = head then true
            else mem tail x

    let removedupes list1 =
        let rec removeduprec list1 list2 =
            match list1 with
            | [] -> list2
            | head :: tail when mem list2 head = false -> removeduprec tail (list2 @ [head])
            | head :: tail -> removeduprec tail list2
        removeduprec list1 []

    let s = Console.ReadLine()
    printfn "%s" (s |> Seq.toList |> removedupes |> List.toArray |> System.String)

    0 // return an integer exit code