#include <iostream>
#include <vector>
using namespace std;

typedef long long ll;

int main()
{
	int W, H, N; vector<vector<bool>> card;
	cin >> W >> H >> N;
	card.resize(W);
	for (int i = 0; i < W; ++i)
		card[i].assign(H, false);
	for (int i = 0; i < N; ++i)
	{
		int s, k;
		cin >> s >> k;
		for (int i = 0; i < W; ++i)
			card[i][k - 1] = true;
		for (int i = 0; i < H; ++i)
			card[s - 1][i] = true;
	}

	ll ans = -N;
	for (int i = 0; i < W; ++i)
	{
		for (int j = 0; j < H; ++j)
		{
			if (card[i][j])
				++ans;
		}
	}

	cout << ans << endl;

	return 0;
}