W = int(raw_input())
H = int(raw_input())
N = int(raw_input())
S,K = set([]),set([])
for num in xrange(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