let () =
  let w, h, n = Scanf.scanf "%d %d %d " (fun w h n -> w, h, n) in
  let a = Array.make w h in
  let rec read i ks =
    if i = n then List.length ks
    else begin
      let s, k = Scanf.scanf "%d %d " (fun s k -> s, k) in
      let s, k = s - 1, k - 1 in
      a.(s) <- a.(s) - 1;
      read (i + 1) (if List.mem k ks then ks else k :: ks)
    end in
  let z = read 0 [] in
  Array.fold_left (fun m e -> m + if e <> h then e else z) 0 a
  |> Printf.printf "%d\n"