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

int row[200005], col[200005], dui1[500005], dui2[500005];

signed main() {
	int n, m, k; cin >> n >> m >> k;
	for (int r, c; k--;) {
		scanf("%lld %lld", &r, &c);
		row[r] = 1;
		col[c] = 1;
		dui1[r - c + max(n, m)] = 1;
		dui2[r + c] = 1;
	}
	int res = 0;
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= m; j++)
			if (!row[i] && !col[j] && !dui1[i - j + max(n, m)] && !dui2[i + j])
				res++;
	cout << res;
	return 0;
}