w=input()
h=input()
n=input()
sk=[tuple(map(int,raw_input().split()))for _ in[0]*n]
r=set()
for c in sk:
	for d in[(c[0],i)for i in range(1,h+1)]:
		r.add(d)
	for d in[(i,c[1])for i in range(1,w+1)]:
		r.add(d)
#print r
for c in sk:
	r.remove(c)
#print r
print len(r)