#coding: utf-8
##yuki_11

w=int(raw_input())
h=int(raw_input())
n=int(raw_input())

ss=set([])
sk=set([])

for i in xrange(n):
 s,k=map(int,raw_input().split())
 ss.add(s)
 sk.add(k)

res=len(ss)*h+len(sk)*w-len(ss)*len(sk)-n

print  res