#include <iostream>
#include <vector>
#include <array>
#include <algorithm>

using namespace std;

#define REP(i,first,last) for (int i=first;i<last;i++)
#define FOR(it,con) for (auto it=con.begin();it!=con.end();it++)
int W,H,N;

int main(){
  cin >> W;
  cin >> H;
  cin >> N;
  vector<bool> w_list(W+1, false);
  vector<bool> h_list(H+1, false);
  int w_val, h_val;
  int w = 0;
  int h = 0;
  REP (i,0,N) {
    cin >> w_val;
    cin >> h_val;
    if (!w_list[w_val]) {
      w_list[w_val] = true;
      w++;
    }
    if (!h_list[h_val]) {
      h_list[h_val] = true;
      h++;
    }
  }
  int amari = (W - w) * (H - h);
  long result = W * H - amari - N;

  cout<<result<<endl;
}