Scanf.scanf "%d" (fun n ->
    let b = Array.init n (fun _ -> Scanf.scanf " %d" (fun b -> b)) in
    let search b =
        let k = Array.length b in
        let rec loop i =
            if i < 0 then None else
                if b.(i) = i + 1 then Some i else loop (i - 1)
        in
        loop (k - 1)
    in
    let remove b x =
        let k = Array.length b in
        let b2 = Array.make (k - 1) 0 in
        let rec loop i j =
            if i = k then b2 else 
                if i = x then loop (i + 1) j else (
                    b2.(j) <- b.(i);
                    loop (i + 1) (j + 1)
                )
        in
        loop 0 0
    in
    let rec loop b i history =
        if i = 0 then history else
            match search b with
            | Some x -> loop (remove b x) (i - 1) ((x + 1) :: history)
            | None -> []
    in
    let k = loop b n [] in
    if k = [] then print_endline "-1" else
        List.iter (Printf.printf "%d\n") k
)