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

using int64 = long long;
constexpr int mod = 998244353;
constexpr int64 infll = (1LL << 62) - 1;
constexpr int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;

template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << p.first << " " << p.second;
  return os;
}

template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  for (int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template<typename T>
istream &operator>>(istream &is, vector<T> &v) {
  for (T &in : v) is >> in;
  return is;
}

template<typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template<typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template<typename T = int64>
vector<T> make_v(size_t a) {
  return vector<T>(a);
}

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t) fill_v(e, v);
}

template<typename F>
struct FixPoint : F {
  explicit FixPoint(F &&f) : F(forward<F>(f)) {}

  template<typename... Args>
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward<Args>(args)...);
  }
};

template<typename F>
inline decltype(auto) MFP(F &&f) {
  return FixPoint<F>{forward<F>(f)};
}

int main() {
  int H, W, N;
  cin >> H >> W >> N;
  auto A = make_v< int >(H, W);
  for(int i = 0; i < N; i++) {
    int a, b;
    cin >> a >> b;
    --a, --b;
    A[a][b] = 1;
  }
  int64 ret = 0;
  vector< int > height(W);
  for(int i = 0; i < H; i++) {
    for(int j = 0; j < W; j++) {
      if(A[i][j]) height[j] = 0;
      else height[j]++;
    }
    vector< pair< int, int > > st;
    int64 aplysia = 0;
    for(int j = 0; j < W; j++) {
      int sz = 1;
      while(not st.empty() and st.back().first >= height[j]) {
        aplysia -= st.back().first * st.back().second;
        sz += st.back().second;
        st.pop_back();
      }
      st.emplace_back(height[j], sz);
      aplysia += st.back().first * st.back().second;
      ret += aplysia;
    }
  }
  cout << ret << endl;
}