/*
 * 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 RX = 1,  RY = 1,  x = 1,  y = 1,  N = 1;

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws IOException {
        while (RX != 0 && RY != 0 && N != 0) {
            str = new StringTokenizer(br.readLine());

            RX = Integer.parseInt(str.nextToken());
            RY = Integer.parseInt(str.nextToken());
            N = Integer.parseInt(str.nextToken());
            pole = new int[RY][RX];
            
            for (int k = 0; k < N; k++) {
                str = new StringTokenizer(br.readLine());
                x = Integer.parseInt(str.nextToken()) - 1;
                y = Integer.parseInt(str.nextToken()) - 1;

                pole[y][x] = 1;
                
                for (int u = 0; u < pole.length; u++) {
                    pole[u][x] = 2;
                }
                for (int u = 0; u < pole[0].length; u++) {
                    pole[y][u] = 2;
                }

                
                for (int u = 0; x - u >= 0 && y - u >= 0; u++) {
                    pole[y - u][x - u] = 2;
                }
                for (int u = 0; x + u < pole[0].length && y + u < pole.length; u++) {
                    pole[y + u][x + u] = 2;

                }
                for (int u = 0; y + u < pole.length && x - u >= 0; u++) {
                    pole[y + u][x - u] = 2;
                }
                for (int u = 0; y - u >= 0 && x + u < pole[0].length; u++) {
                    pole[y - u][x + 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 (RX != 0 && RY != 0) {
                System.out.println(pocet);
            }
        }

    }
}