// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

#include <algorithm>
// #include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
// using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << H << " ";
    debug_out(T...);
}

int main() {
    ll H, W, N;
    cin >> H >> W >> N;
    vector<ll> a(N);
    vector<ll> b(N);
    assert(1 <= H && H <= 3000);
    assert(1 <= W && W <= 3000);
    ll lim_n = min(H * W, 100000LL);
    assert(1 <= N && N <= lim_n);
    map<pll, ll> mp;
    for (ll i = 0; i < N; i++) {
        cin >> a[i] >> b[i];
        assert(1 <= a[i] && a[i] <= H);
        assert(1 <= b[i] && b[i] <= W);
        a[i]--;
        b[i]--;
        assert(mp[pll(a[i], b[i])] == 0);
        mp[pll(a[i], b[i])]++;
    }
    vector<vector<ll>> c(H, vector<ll>(W, 0));
    for (ll i = 0; i < N; i++) {
        c[a[i]][b[i]] = 1;
    }
    vector<vector<ll>> length(H, vector<ll>(W));
    for (ll j = 0; j < W; j++) {
        if (c[H - 1][j] == 0) {
            length[H - 1][j] = 1;
        } else {
            length[H - 1][j] = 0;
        }
    }
    for (ll i = H - 2; i >= 0; i--) {
        for (ll j = 0; j < W; j++) {
            if (c[i][j] == 0) {
                length[i][j] = length[i + 1][j] + 1;
            } else {
                length[i][j] = 0;
            }
        }
    }
    // debug(length);
    ll ans = 0;
    stack<pll> st;
    st.push(pll(-1, -1));
    ll now = 0;
    for (ll i = 0; i < H; i++) {
        for (ll j = 0; j < W; j++) {
            ll idx = j;
            while (st.top().first >= length[i][j]) {
                now -= st.top().first * st.top().second;
                // ans = max(ans, st.top().first * (j - st.top().second));
                idx -= st.top().second;
                st.pop();
            }
            now += length[i][j] * (j - idx + 1);
            ans += now;
            st.push(pll(length[i][j], j - idx + 1));
            // debug_out(now, i, j);
        }
        while (st.size() > 1) {
            // ans = max(ans, st.top().first * (W - st.top().second));
            st.pop();
        }
        now = 0;
    }
    cout << ans << endl;
}