W = int(input())
H = int(input())
N = int(input())
S, K = set(), set()
for i in range(N):
    s, k = map(int, input().split())
    S.add(s)
    K.add(k)
Ns, Nk = len(S), len(K)
print(Ns * H + Nk * W - Ns * Nk - N)