/*
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 * 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 boolean[][] 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) {
            str = new StringTokenizer(br.readLine());

            RX = Integer.parseInt(str.nextToken());
            RY = Integer.parseInt(str.nextToken());
            N = Integer.parseInt(str.nextToken());
            pole = new boolean[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] = true;
                }
                for (int u = 0; u < pole[0].length; u++) {
                    pole[y][u] = true;
                }

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

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

//                for (int i = 0; i < pole.length; i++) {
//                    for (int j = 0; j < pole[0].length; j++) {
//                        System.out.print(pole[i][j]);
//                    }
//                    System.out.println();
//                }

                
            }
            
            
            int pocet = 0;
            for (int u = 0; u < pole.length; u++) {
                for (int v = 0; v < pole[0].length; v++) {
                    if (pole[u][v] == false) {
                        pocet++;
                    }
                }


            }
            if (RX != 0 && RY != 0) {
                System.out.println(pocet);
            }
        }

    }
}