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

suit = set()
number = set()

for i in range(N):
    line = input().split()
    suit.add(int(line[0]))
    number.add(int(line[1]))

result = W * H - (W - len(suit)) * (H - len(number)) - N
print(result)