import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;

public class ith {

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String line;
        line = br.readLine();
        String[] t = line.split(" ");
        int x = Integer.parseInt(t[0]);
        int y = Integer.parseInt(t[1]);
        int n = Integer.parseInt(t[2]);

        boolean[] xchess = new boolean[x];
        boolean[] ychess = new boolean[y];

        int queenx[] = new int[n];
        int queeny[] = new int[n];
        int i = 0;
        while ((line = br.readLine()) != null) {
            if (i == queenx.length) {
                break;
            }
            t = line.split(" ");


            queenx[i] = Integer.parseInt(t[0])-1;
            xchess[queenx[i]] = true;
            queeny[i] = Integer.parseInt(t[1])-1;
            ychess[queeny[i]] = true;
            i++;

        }
        
        int out = 0;

        for (int xpos = 0; xpos < x; xpos++) {
            if (xchess[xpos] == false) {
                for (int ypos = 0; ypos < y; ypos++) {
                    if (ychess[ypos] == false) {
                        boolean flag = true;
                        for (int qindex = 0; qindex < n; qindex++) {
                            if (Math.abs(queenx[qindex]-xpos) == Math.abs(queeny[qindex]-ypos)) {
                                flag = false;
                                break;
                            }
                        }
                        if (flag) out++;
                    }
                }
            }
        }
        System.out.println(out);

    }
}