W = int(input())

H = int(input())

N = int(input())

S = []

K = []

for i in range(N):
    
    s, k = map(int, input().split())
    
    S += [s]
    
    K += [k]
    
s = len(set(S))

k = len(set(K))

print(s * H + k * W - s * k - N)