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

num_s = len(set([x for x,_ in SK]))
num_k = len(set([x for _,x in SK]))

print(num_s * H + (W - num_s) * num_k - N)