#include <bits/stdc++.h>
#define debug(x) cerr << #x << ": " << x << endl
#define debugArray(x, n)                           \
  for (long long hoge = 0; (hoge) < (n); ++(hoge)) \
  cerr << #x << "[" << hoge << "]: " << x[hoge] << endl
using namespace std;

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  long long W, H, N;
  cin >> W >> H >> N;
  set<int> Sw, Sh;
  for (int i = 0; i < N; i++) {
    int S, K;
    cin >> S >> K;
    Sw.insert(S);
    Sh.insert(K);
  }
  cout << W * H - (W - Sw.size()) * (H - Sh.size()) - N << endl;
  return 0;
}