W = int(input())
H = int(input())
N = int(input())
S = set()
K = set()

for i in range(N):
    s, k = map(int,input().split())
    S.add(s)
    K.add(k)

CW = len(S)
CH = len(K)

print(W*H-(W-CW)*(H-CH)-N)