#include <iostream>
#include <set>

using lint = long long;

void solve() {
    lint w, h;
    std::cin >> w >> h;

    int n;
    std::cin >> n;

    std::set<int> xs, ys;
    for (int i = 0; i < n; ++i) {
        int x, y;
        std::cin >> x >> y;
        xs.insert(x);
        ys.insert(y);
    }

    std::cout << w * h - (w - xs.size()) * (h - ys.size()) - n
              << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}