Scanf.scanf "%d" (fun n ->
    let x = Array.init n (fun _ -> Scanf.scanf " %d" (fun x -> x)) in
    Array.sort compare x;

    let rec loop i =
        if i = n then "YES" else
            if x.(i) - x.(i - 1) = x.(i - 1) - x.(i - 2) then loop (i + 1)
            else "NO"
    in
    (if x.(0) = x.(1) then "NO" else loop 2) |> print_endline
)