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

int main()
{
	LL W, H, ans;
	int N, S, K;
	unordered_set<int> Sset, Kset;
	cin >> W >> H >> N;

	for (int i = 0; i < N; ++i)
	{
		cin >> S >> K;
		Sset.insert(S);
		Kset.insert(K);
	}

	ans = -N;
	for (int w = 1; w <= W; ++w)
	{
		for (int h = 1; h <= H; ++h)
		{
			auto sit = Sset.find(w);
			auto kit = Kset.find(h);
			if (sit != Sset.end() || kit != Kset.end())
				++ans;
		}
	}

	cout << ans;

	return 0;
}