#include <iostream>
#include <algorithm>
#include <cstring>
#include <climits>
#define W_MAX 1000000
#define H_MAX 1000000
#define N_MAX 100
using namespace std;
typedef long long LL;

typedef struct
{
	int S;
	int K;
} Card;

bool compS(const Card& x, const Card& y)
{
	return x.S < y.S;
}

bool compK(const Card& x, const Card& y)
{
	return x.K < y.K;
}

int main()
{
	LL W, H, N, Bs, Bk;
	Card hand[N_MAX];
	cin >> W >> H >> N;

	for (int i = 0; i < N; ++i)
	{
		cin >> hand[i].S >> hand[i].K;
	}

	sort(hand, hand + N, compS);
	Bs = hand[0].S - hand[N - 1].S + W - 1;
	for (int i = 1; i < N; ++i)
	{
		LL temp = hand[i].S - hand[i - 1].S;
		if (temp >=2 )
			Bs += temp - 1;
	}

	sort(hand, hand + N, compK);
	Bk = hand[0].K - hand[N - 1].K + H - 1;
	for (int i = 1; i < N; ++i)
	{
		LL temp = hand[i].K - hand[i - 1].K;
		if (temp >= 2)
			Bk += temp - 1;
	}

	cout << (W*H) - (Bs*Bk) - N;

	return 0;
}