#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < n; ++i)
using ll = long long;
using P = pair<int,int>;
int main() {
   ll W,H,N;cin>>W>>H>>N;
   set<ll> mark,num;
   rep(i,N){
      ll Si,Ki;cin>>Si>>Ki;
      mark.insert(Si);
      num.insert(Ki);
   }
   cout<<H*mark.size()+W*num.size()-N-mark.size()*num.size()<<endl;
}