#include <iostream>
#include <algorithm>
#include <cstdio>
#include <string>
#include <vector>

using namespace std;

#define ll long long

int main(){

   ll w,h,n;
   cin>>w>>h>>n;
   int s[100],k[100];
   vector<ll> W(w+1),H(h+1);
   fill(W.begin(),W.end(),1);
   fill(H.begin(),H.end(),1);
   W[0]=H[0]=0;
   for(int i=0;i<n;++i){
       cin>>s[i]>>k[i];
       W[s[i]]=0;
       H[k[i]]=0;
   }

   ll sw=0,sh=0; //除く和
   for(int i=0;i<=w;++i) sw+=W[i];
   for(int i=0;i<=h;++i) sh+=H[i];
   cout<<w*h-n-sw*sh<<endl;

   return 0;
}