//JAVA15: import java.io.; import java.util.; import java.util.stream.*;

class Result {

public static int queensAttack(int n, int k, int r_q, int c_q, List<List<Integer>> obstacles) {
    Set<String> obstacleSet = new HashSet<>();
    for (List<Integer> obs : obstacles) {
        obstacleSet.add(obs.get(0) + "-" + obs.get(1));
    }

    int[][] directions = {
        {-1, 0}, {1, 0}, {0, -1}, {0, 1},   // vertical and horizontal
        {-1, -1}, {-1, 1}, {1, -1}, {1, 1}  // diagonals
    };

    int attackableSquares = 0;

    for (int[] dir : directions) {
        int r = r_q + dir[0];
        int c = c_q + dir[1];

        while (r >= 1 && r <= n && c >= 1 && c <= n && !obstacleSet.contains(r + "-" + c)) {
            attackableSquares++;
            r += dir[0];
            c += dir[1];
        }
    }

    return attackableSquares;
}

}

public class Solution { public static void main(String[] args) throws IOException { BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in)); BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

    String[] firstMultipleInput = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");
    int n = Integer.parseInt(firstMultipleInput[0]);
    int k = Integer.parseInt(firstMultipleInput[1]);

    String[] secondMultipleInput = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");
    int r_q = Integer.parseInt(secondMultipleInput[0]);
    int c_q = Integer.parseInt(secondMultipleInput[1]);

    List<List<Integer>> obstacles = new ArrayList<>();

    IntStream.range(0, k).forEach(i -> {
        try {
            obstacles.add(
                Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" "))
                    .map(Integer::parseInt)
                    .collect(Collectors.toList())
            );
        } catch (IOException ex) {
            throw new RuntimeException(ex);
        }
    });

    int result = Result.queensAttack(n, k, r_q, c_q, obstacles);

    bufferedWriter.write(String.valueOf(result));
    bufferedWriter.newLine();

    bufferedReader.close();
    bufferedWriter.close();
}

}