import java.util.Scanner;

public class No11 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int w, h, n;
        long ans = 0;
        w = sc.nextInt();
        h = sc.nextInt();
        n = sc.nextInt();
        int[] s = new int[n], k = new int[n];
        boolean[][] po = new boolean[w][h];

        for (int i = 0; i < n; i++) {
            s[i] = sc.nextInt() - 1;
            k[i] = sc.nextInt() - 1;
            po[s[i]][k[i]] = true;
        }

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < h; j++) {
                if(!po[s[i]][j]){
                    ans++;
                    po[s[i]][j] = true;
                }
            }
            for (int j = 0; j < w; j++) {
                if(!po[j][k[i]]){
                    ans++;
                    po[j][k[i]] = true;
                }
            }
        }

        System.out.println(ans);
    }
}