let s = stdin.ReadLine ()

if s |> Seq.sort |> Seq.map string |> String.concat "" = "abcdefghijklm" then
    "abcdefghijklm" |> Seq.iter (printfn "%c")
else
    let count =
        [|
            for i in "abcdefghijklm" ->
                s |> Seq.filter ((=)i) |> Seq.length
        |]
    if count |> Array.filter ((=)1) |> Array.length = 11 then
        count |> Array.findIndex ((=)0) |> (Array.get <| Array.ofSeq "abcdefghijklm") |> printfn "%c"
    else
        printfn "Impossible"