def main():
    W = int(input())
    H = int(input())
    N = int(input())
    hands = [tuple(map(int, input().split())) for _ in range(N)]
    suits = set(card[0] for card in hands)
    numbers = set(card[1] for card in hands)

    match_candidate = len(suits) * H + len(numbers) * \
        W - len(suits) * len(numbers)
    print(match_candidate - len(hands))


if __name__ == "__main__":
    main()