Scanf.scanf "%d" (fun n ->
    let t =
        let rec loop i acc =
            if i = n then acc else
                loop (i + 1) (Scanf.scanf " %d" (fun d -> acc lor (1 lsl d)))
        in
        loop 0 0
    in
    let rec loop i acc =
        let check o = t land (1 lsl ((i + o) mod 12)) = 0 in
        if i = 12 then acc else
            let acc = if check 1 && check 3 && check 6 && check 8 && check 10 then i :: acc else acc in
            loop (i + 1) acc
    in
    Printf.printf "%d\n" @@ match loop 0 [] with
    | [ a ] -> a
    | _ -> -1
)