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

suit = []
number = []

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

result = W * H - (W - len(suit_set)) * (H - len(number_set)) - N
print(result)