#include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<vector>
#include<set>
#include<list>
#include<queue>
#include<math.h>
#include<bitset>
using ll = long long;
using namespace std;

int main(){
    int w, h, n;
    ll ans = 0;
    cin >> w >> h >> n;
    int suit_n = w, num_n = h;
    vector<int> suit(w), num(h);
    for (int i = 0; i < n; i++){
        int s, k;
        cin >> s >> k;
        if (suit[s-1]){
            if (!num[k-1]){
                num[k-1]++;
                if (num_n) num_n--;
            }
        } else {
            if (num[k-1]){
                suit[s-1]++;
                if (suit_n) suit_n--;
            } else {
                suit[s-1]++;
                num[k-1]++;
                if (num_n) num_n--;
                if (suit_n) suit_n--;
            }
        }
    }

    cout << w*h - num_n*suit_n - n << endl;
}