import java.util.*;
import java.util.stream.*;
import static java.lang.Math.*;
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> sSet=new HashSet<>();
		Set<Integer> kSet=new HashSet<>();
		for(int i=0;i<n;i++){
			sSet.add(sc.nextInt());
			kSet.add(sc.nextInt());
		}
		long ans=0;
		ans+=sSet.size()*h;
		ans+=kSet.size()*w;
		ans-=sSet.size()*kSet.size();
		ans-=n;
		put(ans);
		
	}
	public static void print(Object object){
        System.out.print(object);
    }
    public static void put(Object object) {
        System.out.println(object);
    }
    public static void put(){
        System.out.println();
    }
 
    public static void print(String format,Object... args){
        System.out.print(String.format(format,args));
    }
    public static void put(String format,Object... args) {
        System.out.println(String.format(format,args));
    }
}