w = int(input())
h = int(input())
n = int(input())
W = set()
H = set()
ans = 0
for _ in range(n):
    s, k = map(int, input().split())
    W.add(s)
    H.add(k)

ans = h * w - (h - len(H)) * (w - len(W)) - n
print(ans)