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();
        HashSet<Integer> suits = new HashSet<>();
        HashSet<Integer> numbers = new HashSet<>();
        for (int i = 0; i < n; i++) {
            suits.add(sc.nextInt());
            numbers.add(sc.nextInt());
        }
        long ans = suits.size() * ((long)h - numbers.size()) + numbers.size() * w - n;
        System.out.print(ans);
    }
}