#include <bits/stdc++.h>
using namespace std;

int main() {
	int w,h, n;
	cin >> w >> h >> n;
	vector<int> s(n), k(n);
	for (int i = 0;i < n;i++) {
		cin >> s[i] >> k[i];
	}

	set<int>sets, setk;
	for (int i = 0;i < n;i++) {
		sets.insert(s[i]);
		setk.insert(k[i]);
	}
	set<pair<int, int>>ans;
	for (auto x : sets) {
		for (int i = 1;i <= h;i++) {
			ans.insert({ x,i });
		}
	}
	for (auto x : setk) {
		for (int i = 1;i <= w;i++) {
			ans.insert({ i,x });
		}
	}
	cout << ans.size() - n << endl;


	return 0;
}