import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Scanner;
import java.util.Set;

public class Main {
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int W = sc.nextInt();
		final int H = sc.nextInt();
		final int N = sc.nextInt();
		
		int[] counts = new int[W];
		Set<Integer> numbers = new HashSet<Integer>();
		
		for(int i = 0; i < N; i++){
			final int S = sc.nextInt() - 1;
			final int K = sc.nextInt() - 1;
			
			counts[S]++;
			numbers.add(K);
		}
		
		long sum = (long)(W) * (long)(H);
		for(int i = 0; i < W; i++){
			if(counts[i] == 0){
				sum -= H - numbers.size();
			}else{
				sum -= counts[i];
			}
		}
		
		System.out.println(sum);
	}
	
}