defmodule Main do
  def main do
    IO.read(:line)

    IO.read(:line)
    |> String.split()
    |> Enum.map(&String.to_integer/1)
    |> solve
    |> IO.puts()
  end

  def solve(x) do
    d =
      x
      |> Enum.sort()
      |> each_cons_2
      |> Enum.map(fn {a, b} -> b - a end)

    cond do
      d |> Enum.uniq() |> length <= 1 && d |> hd != 0 -> "YES"
      true -> "NO"
    end
  end

  def each_cons_2(l) do
    [l |> Enum.slice(0..-2), l |> Enum.slice(1..-1)]
    |> Enum.zip()
  end
end