W = int(input())
H = int(input())
N = int(input())

cards = []
for i in range(W):
    for j in range(H):
        cards.append([i + 1, j + 1])
    
my_cards = []
for i in range(N):
    my_cards.append(list(map(int, input().split())))

for my_card in my_cards:
    if my_card in cards:
        cards.remove(my_card)
        
temp = []
for my_card in my_cards:
    for card in cards:
        if my_card[0] == card[0]:
            temp.append(card)
        else:
            if my_card[1] == card[1]:
                temp.append(card)

result = []
for arr in temp:
    if arr not in result:
        result.append(arr)
        
print(len(result))