W = int(input())
H = int(input())
N = int(input())
SK = [list(map(int, input().split())) for _ in range(N)]

ss = set()
ks = set()
for i in range(N):
    s, k = SK[i]
    s -= 1
    ss.add(s)
    ks.add(k)
    
ans = H * len(ss)
ans += W * len(ks) - len(ks) * len(ss)
ans -= N
print(ans)