def main
  w = gets.to_i
  h = gets.to_i
  n = gets.to_i
  cards = Array.new(h){Array.new(w, 0)}
  n.times do
    s,k = gets.split.map(&:to_i)
    cards[k-1][s-1] = 2
    (0...h).each do |_h|
      cards[_h][s-1] = 1 if cards[_h][s-1] != 2
    end
    (0...w).each do |_w|
      cards[k-1][_w] = 1 if cards[k-1][_w] != 2
    end
    cards[k-1][s-1] = 2
  end
  puts cards.flatten.count {|c| c == 1 }
end

main()