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