defmodule Main do
  def main do
    w = IO.read(:line) |> String.trim() |> String.to_integer()
    h = IO.read(:line) |> String.trim() |> String.to_integer()
    n = IO.read(:line) |> String.trim() |> String.to_integer()
    {s, k} = for _ <- 0..(n - 1) do
      IO.read(:line) |> String.trim() |> String.split(" ") |> Enum.map(&String.to_integer/1)
    end
    |> Enum.reduce({[], []}, fn [s, k], {sq, kq} -> {[s | sq], [k | kq]} end)
    s = s |> Enum.uniq() |> length()
    k = k |> Enum.uniq() |> length()
    IO.puts(w * k + s * h - s * k - n)
  end
end