#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <set>
#include <list>
using namespace std;


int main(int argc, const char * argv[]) {
    long long W;
    cin >> W;
    long long H;
    cin >> H;
    int N;
    cin >> N;
    set<int> uniqueW;
    set<int> uniqueH;
    int tmp;
    for (int i = 0; i < N; i++) {
        cin >> tmp;
        uniqueW.insert(tmp);
        cin >> tmp;
        uniqueH.insert(tmp);
    }
    //オーバーフロー
    long long result;
    //
    result = W*H -(W-uniqueW.size())*(H-uniqueH.size())-N;
    cout << result;
    cout << "\n";
}