#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <iomanip>
using namespace std;
#define INF 1e9
#define PI acos(-1)
typedef long long ll;


int main() {
	int w, h, n;
	cin >> w >> h >> n;

	set <int> mark, num;

	ll sum = w*h;
	ll marksum = 0, numsum = 0;

	for (int i = 0; i < n; i++){
		int s, k;
		cin >> s >> k;
		if (mark.count(s) == 0) {
			marksum++;
			mark.insert(s);
		}
		if (num.count(k) == 0) {
			numsum++;
			num.insert(k);
		}
	}

	sum -= (w - marksum)*(h-numsum);
	sum -= n;

	cout << sum << endl;

	return 0;
}