package no011;

import java.util.HashSet;
import java.util.Scanner;

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();
		HashSet<Integer> S = new HashSet<>();
		HashSet<Integer> K = new HashSet<>();
		for(int i=0;i<n;i++) {
			int s = sc.nextInt();
			int k = sc.nextInt();
			S.add(s);
			K.add(k);
		}
		System.out.println((long) S.size() * h + (long) K.size() * w - n - (long) S.size() * K.size());
	}

}