inpl = lambda: list(map(int,input().split()))
W = int(input())
H = int(input())
N = int(input())
hset = set()
wset = set()
for _ in range(N):
    w, h = inpl()
    wset.add(w)
    hset.add(h)
Lh = len(hset)
Lw = len(wset)
print(Lh*W + H*Lw - Lh*Lw - N)