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

public class No11 {

	public static void main(String[] args) throws IOException{
		//カードマッチ
		String[] text = readStr();
		int W = Integer.parseInt(text[0]);
		int H = Integer.parseInt(text[1]);
		int N = Integer.parseInt(text[2]);
		int S , K;
		Long count = 0l;
		ArrayList<Integer> wlist = new ArrayList<>() , hlist = new ArrayList<>();
		
		for(int i = 0;i < N;i++) {
			S = Integer.parseInt(text[i + 3].split(" ")[0]);
			K = Integer.parseInt(text[i + 3].split(" ")[1]);
			
			if(!wlist.contains(S)) wlist.add(S);
			if(!hlist.contains(K)) hlist.add(K);
			
		}
		count = Math.multiplyExact((long)(W - wlist.size()), H - hlist.size());
		System.out.println(Math.multiplyExact((long)W, H) - count - N);

	}
	
	public static String[] readStr() throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		ArrayList<String> list = new ArrayList<>();

		do {
			list.add(br.readLine());
		}while(br.ready());

		br.close();

		String[] text = new String[list.size()];
		list.toArray(text);

		return text;

	}

}