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

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

    vector<vector<int>> defects(h, vector<int>(w));
    for(int i = 0; i < n; ++i) defects[a[i]][b[i]] = 1;

    vector<int> dp(w);
    int ans = 0;

    for(int i = 0; i < h; ++i) {
        vector<tuple<int, int, int>> x;
        for(int j = 0; j < w; ++j) {
            if(defects[i][j]) {
                dp[j] = 0;
                x.clear();
                continue;
            }
            dp[j]++;
            int k = dp[j];
            int t = 1;
            while(!x.empty()) {
                auto [l, w, s] = x.back();
                if(l < k) break;
                t += w;
                x.pop_back();
            }

            if(x.empty()) {
                x.push_back({k, t, k * t});
                ans += k * t;
            } else {
                auto [l, w, s] = x.back();
                x.push_back({k, t, s + k * t});
                ans += s + k * t;
            }
        }
    }
    cout << ans << endl;
}