#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);
    vector<vector<bool>> table(W, vector<bool>(H, false));
    for (int i = 0; i < N; ++i) {
        cin >> S[i] >> K[i];
        table[S[i] - 1][K[i] - 1] = true;
    }

    ll res = 0;
    for (ll i = 0; i < W; ++i) {
        if (find(S.begin(), S.end(), i + 1) != S.end()) {
            for (ll j = 0; j < H; ++j) {
                if (!table[i][j]) {
                    ++res;
                    table[i][j] = true;
                }
            }
        }
    }
    for (ll j = 0; j < H; ++j) {
        if (find(K.begin(), K.end(), j + 1) != K.end()) {
            for (ll i = 0; i < W; ++i) {
                if (!table[i][j]) {
                    ++res;
                    table[i][j] = true;
                }
            }
        }
    }

    cout << res << endl;
}