let solve a b c d =
    let lst = [ a; b; c; d; ] |> List.sort ( - ) in
    let rec solve' cur left_lst =
        match left_lst with
        | x :: xs ->
            if x - cur <> 1 then
                "No"
            else
                solve' x xs
        | _ -> "Yes"
    in
    solve' (List.hd lst) (List.tl lst)

let () =
    let a, b, c, d =
        read_line ()
        |> fun l -> Scanf.sscanf l "%d %d %d %d" (fun a b c d -> (a, b, c, d))
    in
    print_endline @@ solve a b c d