#include <iostream>
#include <vector>
#include <set>
using namespace std;
int main(){
	int W;
	cin >> W;
	int H;
	cin >> H;
	int N;
	cin >> N;
	vector<int> S(N);
	vector<int> K(N);
	for (int i = 0; i < N; i++){
		cin >> S[i] >> K[i];
	}
	set<int> st1;
	for (int i = 0; i < N; i++){
		st1.insert(S[i]);
	}
	set<int> st2;
	for (int i = 0; i < N; i++){
		st2.insert(K[i]);
	}
	int A = st1.size();
	int B = st2.size();
	cout << A * H + B * W - A * B - N << endl;
}