defmodule Main do
  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 main do
    [n, m] = li()

    map = for i <- 1..n, into: %{}, do: {i, 0}
    for _ <- 1..m, reduce: map do
      m ->
        [_a, b] = li()
        Map.update!(m, b, fn v -> v+1 end)
    end
    |> Enum.count(fn {_, v} -> v == 0 end)
    |> IO.puts
  end
end