import java.math.BigInteger;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int W = scanner.nextInt();
		int H = scanner.nextInt();
		int N = scanner.nextInt();
		Set<Integer> Wsum = new HashSet<>();
		Set<Integer> Hsum = new HashSet<>();
		for (int i = 0; i < N; i++) {
			int S = scanner.nextInt();
			int K = scanner.nextInt();
			Wsum.add(S);
			Hsum.add(K);
		}
		System.out.println(W * H - (W - Wsum.size()) * (H - Hsum.size()) - N);
	}

}