#!/usr/bin/python
w = int(raw_input())
h = int(raw_input())
n = int(raw_input())
sks = [map(int, raw_input().split()) for _ in xrange(n)]
rows = len({e[0] for e in sks})
cols = len({e[1] for e in sks})
res = rows * h + cols * w - rows * cols - n
print res