/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.util.StringTokenizer;
/**
 *
 * @author cteam05
 */
public class ith {
static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
static StringTokenizer str;
static int[][] pole;
static int x=1,y=1,i=1,j=1,N =1;
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws IOException {
       while(x!=0&&y!=0&&N!=0){
        str=new StringTokenizer(br.readLine());
       
        x = Integer.parseInt(str.nextToken());
        y =  Integer.parseInt(str.nextToken());
         N=Integer.parseInt(str.nextToken());
           pole=new int [y][x];
        for(int k=0;k<N;k++){
            str=new StringTokenizer(br.readLine());
           i= Integer.parseInt(str.nextToken())-1;
            j= Integer.parseInt(str.nextToken())-1;
            
          pole[j][i]=1;
          for(int u=0;u<pole.length;u++){
              pole[u][i]=2;
          }
          for(int u=0;u<pole[0].length;u++){
              pole[j][u]=2;
          } 
          int rozdil= i  -j ;
          for(int u=0; i - u>=0&&j-u>=0;u++){
              pole[j-u][i-u]=2;
              
          }
           for(int u=0;  i  + u<pole.length&&j +u<pole[0].length;u++){
              pole[j+u][i+u]=2;
              
          }
          for(int u=0;i+u<pole.length&&j-u>=0;u++){
              pole[i+u][j-u]=2;
          }
          for(int u=0;i-u>=0&&j+u<pole[0].length;u++){
              pole[i-u][j+u]=2;
          }
////          for(int u=0;u<pole.length;u++){
////              if(u+max<pole.length){
////              pole[u+max][u]=2;
////              }
////          }
////           for(int u=pole.length;u>=0;u--){
////              if(u+max<pole[0].length&&u>0){
////              pole[pole.length-uu+max]=2;
////              }
////          }
          
       
            
        }
           int pocet=0;
            for(int u=0;u<pole.length;u++){
              for(int v=0;v<pole[0].length;v++){
                  if(pole[u][v]==0){
                      pocet++;
                  }
              }
             
           
            }
           if(x!=0&&y!=0&&N!=0){
            System.out.println(pocet);
           }
    }
        
        }
    
}