#include <iostream>
#include <set>
using namespace std;
int main()
{
    long long W, H, N;
    while (cin>>W>>H>>N) {
        set<int> w, h;
        for(int i=0;i<N;++i) {
            int a, b; cin>>a>>b;
            w.insert(a);
            h.insert(b);
        }
        cout<<W*H-(W-w.size())*(H-h.size())-N<<endl;
    }
}