import java.util.*;
import java.math.*;
import java.io.*;
 
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();
		long sum = 0;
		int[] W = new int[w];
		int[] H = new int[h];
		int uh = 0;
		int uw = 0;
		for(int i = 0; i < n; i++) {
			int s = sc.nextInt()-1;
			int k = sc.nextInt()-1;
			if(W[s] == 0) uw++;
			if(H[k] == 0) uh++;
		}
		System.out.println((long)w * h - (w - uw) * (h - uh) - n);
		
		
		
	}	
	
}