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

mark = set()
number = set()

for _ in range(N):
    w, h = map(int, input().split())
    mark.add(w)
    number.add(h)

total = len(mark) * H + len(number) * W - len(mark) * len(number)

print(total - N)