let solve dlst =
  let rec solve' lst cur =
    match lst with
    | [] -> 10
    | x::xs ->
      if x <> cur then cur
      else solve' xs (cur + 1)
  in
  solve' dlst 1

let () =
  let blst = read_line ()
             |> Str.split (Str.regexp_string " ")
             |> List.map int_of_string
  in
  solve blst
  |> string_of_int
  |> print_endline