#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

template <typename T>
vector<T> uni(vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}

int main() {
    long long w, h, n; cin >> w >> h >> n;
    vector<int> s(n), k(n);
    for (int i = 0; i < n; i++) cin >> s[i] >> k[i];
    long long cnt_s = uni(s).size();
    long long cnt_k = uni(k).size();
    long long match = cnt_s * h + w * cnt_k - cnt_s * cnt_k;
    cout << match - n << endl;
    return 0;
}