import java.io.*;
import java.util.*;

public class ith {
	
	
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		//BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int X,Y,N,counter = 0;
		
		while(true){
			counter = 0;
			X = sc.nextInt(); //1
			Y = sc.nextInt(); //1
			N = sc.nextInt(); //0
			if(X==0 && Y==0 && N==0) {break;}
			
			int [] Nx = new int[N];
			int [] Ny = new int[N];
			
			for (int i = 0; i<N; i++) {
				Nx[ i ] = sc.nextInt()-1;
				Ny[ i ] = sc.nextInt()-1;
			}	
			
			boolean queens = false;
			
			for (int i=0; i<X; i++) {
				for (int j=0; j<Y; j++) {			
						queens = true;	
						for (int k=0; k<N; k++) {						
							if(isFree(i, j, Nx[k],Ny[k])) {
								queens=true;
							} else {
								queens=false;
								break;
							}						
						}	
						if(queens){
							counter++;
						}
				}
			}
			
			System.out.println(counter);		
		}
	}
	
	
	public static boolean isFree(int x,int y,int dx, int dy) {
		int L = Math.abs(dx-dy);
		int P = dx+dy;
		
		if (x==dx || y==dy) return false;
		if ((x + L)==y) return false;
		if ((P - x)==y) return false;
		
		return true;
	}
	
}