#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint998244353;
//const int mod = 998244353;
//using mint = modint1000000007;
//const int mod = 1000000007;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int h, w, n; cin >> h >> w >> n;
	vector table(h, vector<int>(w));
	set<P>st;
	rep(i, n) {
		int a, b; cin >> a >> b;
		a--, b--;
		st.insert({ a,b });
	}
	rep(i, h)rep(j, w) {
		if (st.count({ i,j }))continue;
		if (0 != j)table[i][j] = table[i][j - 1] + 1;
		else table[i][j] = 1;
	}
	long long ans = 0;
	rep(j, w) {
		long long sub = 0;
		vector<pair<int, int>>v;
		rep(i, h) {
			pair<int, int> p = { table[i][j],1 };
			while (!v.empty() && v.back().first >= table[i][j]) {
				auto back = v.back();
				v.pop_back();
				sub -= back.first * back.second;
				p.second += back.second;
			}
			sub += p.first * p.second;
			v.push_back(p);
			ans += sub;
		}
	}
	cout << ans << endl;
	return 0;
}