#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long ll;

int main(){
    ll W, H, N;
    cin >> W >> H >> N;
    vector<ll> S(N), K(N);
    for (int i = 0; i < N; ++i) {
        cin >> S[i] >> K[i];
    }

    sort(S.begin(), S.end());
    sort(K.begin(), K.end());
    S.erase(unique(S.begin(), S.end()), S.end());
    K.erase(unique(K.begin(), K.end()), K.end());

    ll res = S.size() * H + W * K.size() - S.size() * K.size() - N;
    cout << res << endl;
}