from collections import defaultdict

w = int(input())
h = int(input())
n = int(input())

M, K = set(), set()
for _ in range(n):
    m, k = map(int, input().split())
    M.add(m)
    K.add(k)

print(len(M) * h + len(K) * w - len(M) * len(K) - n)