structure Set =
struct
datatype 'a tree = Leaf | Node of 'a * 'a tree * 'a tree

val empty = Leaf

fun size Leaf = 0
  | size (Node (v, left, right)) = 1 + size left + size right

fun add Leaf newV = Node (newV, Leaf, Leaf)
  | add (Node (nodeV, left, right)) newV =
    if nodeV = newV then (Node (nodeV, left, right))
    else if nodeV < newV then Node (nodeV, left, add right newV)
    else Node (nodeV, add left newV, right)

end


fun readInt () =
    valOf (TextIO.scanStream (Int.scan StringCvt.DEC) TextIO.stdIn)


val () =
    let
        val w = Int.toLarge (readInt ())
        val h = Int.toLarge (readInt ())
        val n = readInt ()
        val sk_s = List.tabulate (n, fn _ => (readInt (), readInt()))

        val (s_s, k_s) =
            List.foldl
                (fn ((s, k), (accS, accK)) =>
                    (Set.add accS s, Set.add accK k))
                (Set.empty, Set.empty)
                sk_s

        val ans = h * w - (w - (Int.toLarge (Set.size s_s))) * (h - (Int.toLarge (Set.size k_s))) - (Int.toLarge n)
    in
        print (LargeInt.toString ans ^ "\n")
    end