defmodule Main do
  @spec input() :: binary()
  def input, do: IO.read(:line) |> String.trim
  def ii, do: input() |> String.to_integer
  def li, do: input() |> String.split |> Enum.map(&String.to_integer/1)
  def yn(b), do: IO.puts (if b, do: "Yes", else: "No")

  def pow(x, n, mod) do
    cond do
      n == 0 -> 1
      rem(n, 2) == 0 ->
        y = pow(x, div(n, 2), mod)
        rem(y * y, mod)
      true ->
        rem(x * pow(x, n - 1, mod), mod)
    end
  end

  @mod 998244353

  def inv(x) do
    pow(x, @mod-2, @mod)
  end

  def main do
    n = ii()
    cs = input() |> String.graphemes()

    ab = cs |> Enum.count(&(&1 == "A" || &1 == "B"))
    for i <- 1..ab//1, reduce: 1 do
      acc ->
        x = rem(acc * inv(i), @mod)
        rem(x * (n - i + 1), @mod)
    end
    |> IO.puts
  end
end