#!/usr/bin/env python3
import itertools
import sys

W = int(input())
H = int(input())
N = int(input())
Shand = [False] * (W + 1)
Khand = [False] * (H + 1)
count = 0
Shand[0] = True
Khand[0] = True
rest = []
for line in sys.stdin:
    S, K = map(int, line.split())
    Shand[S] = True
    Khand[K] = True
for s, k in itertools.product(Shand, Khand):
    if s or k:
        continue
    count += 1
    rest.append((s, k))
print(W * H - count - N)