#!/usr/bin/env python3
import sys
input = sys.stdin.readline

w = int(input())
h = int(input())
n = int(input())
suit = set()
number = set()
for _ in range(n):
    s, k = map(int, input().split())
    suit.add(s)
    number.add(k)
ans = len(suit) * h + len(number) * w
ans -= len(suit) * len(number)
ans -= n

print(ans)