import java.util.*;
 

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int W = sc.nextInt();
		int H = sc.nextInt();
		int N = sc.nextInt();
		Set<Integer> a = new HashSet<>();
		Set<Integer> b = new HashSet<>();
		for(int i=0;i<N;i++){
			a.add(sc.nextInt());
			b.add(sc.nextInt());
		}
		System.out.println(a.size()*H+b.size()*W-a.size()*b.size()-N);
		
	}
}