W = int(input())
H = int(input())
N = int(input())
sset = set()
kset = set()
for _ in range(N):
    s, k = map(int, input().split())
    sset.add(s)
    kset.add(k)
a = H*W
a -= (W-len(sset))*(H-len(kset))
print(a-N)