#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

LL W, H;
set<int> CW;
set<int> CH;

int main() {
    cin >> W >> H;
    LL N; cin >> N;
    rep(i, N) {
        LL w, h; cin >> w >> h;
        CW.insert(w);
        CH.insert(h);
    }

    LL ans = W * H - (W - CW.size()) * (H - CH.size()) - N;
    cout << ans << endl;

    return 0;
}