import java.util.ArrayList;
import java.util.HashSet;

public class PageLayout {


    private static ArrayList<HashSet<Integer>> fitting_stories;
    private static int[] areas;
    private static int N;


    public static void main(String[] args) {
        Kattio kat = new Kattio(System.in);
        while (true) {
            N = kat.getInt();
            if (N == 0)
                break;
            ArrayList<int[]> stories = new ArrayList<>();
            for (int i = 0; i < N; i++) {
                int[] line = new int[4];
                line[0] = kat.getInt();
                line[1] = kat.getInt();
                line[2] = kat.getInt();
                line[3] = kat.getInt();
                stories.add(line);
            }
            areas = new int[N];
            for (int i = 0; i < N; i++) {
                areas[i] = story_size(stories.get(i));
            }
            fitting_stories = new ArrayList<>();
            for (int i = 0; i < N; i++) {
                fitting_stories.add(new HashSet<>());
            }
            for (int i = 0; i < N; i++) {
                fitting_stories.get(i).add(i);
                for (int j = i + 1; j < N; j++) {
                    if (fit_together(stories.get(i), stories.get(j))) {
                        fitting_stories.get(i).add(j);
                        fitting_stories.get(j).add(i);
                    }
                }
            }
            kat.println(opti_page(0, 0));
            kat.flush();
        }
    }


    static int story_size(int[] story) {
        return story[0] * story[1];
    }


    static boolean fit_together(int[] story1, int[] story2) {
        int w1 = story1[0];
        int h1 = story1[1];
        int x1 = story1[2];
        int y1 = story1[3];
        int w2 = story2[0];
        int h2 = story2[1];
        int x2 = story2[2];
        int y2 = story2[3];
        if (x1 < x2) {
            if (x1 + w1 > x2) {
                if (y1 < y2) {
                    if (y1 + h1 > y2) {
                        return false;
                    }
                } else if (y2 < y1) {
                    if (y2 + h2 > y1) {
                        return false;
                    }
                } else {
                    return false;
                }
            }
        } else if (x2 < x1) {
            if (x2 + w2 > x1) {
                if (y1 < y2) {
                    if (y1 + h1 > y2) {
                        return false;
                    }
                } else if (y2 < y1) {
                    if (y2 + h2 > y1) {
                        return false;
                    }
                } else {
                    return false;
                }
            }
        } else {
            if (y1 < y2) {
                if (y1 + h1 > y2) {
                    return false;
                }
            } else if (y2 < y1) {
                if (y2 + h2 > y1) {
                    return false;
                }
            } else {
                return false;
            }
        }
        return true;
    }


    static int opti_page(int current_story, int current_page) {
        if (current_story == N)
            return 0;

        int prev_area = opti_page(current_story + 1, current_page);
        for (int j = 0; j < current_story; j++) {
            if ((current_page >> j) % 2 == 1) {
                if (!fitting_stories.get(j).contains(current_story)){
                    return prev_area;
                }
            }
        }
        int new_area = opti_page(current_story + 1, current_page | 1 << current_story) + areas[current_story];

        if (new_area > prev_area) {
            return new_area;
        } else {
            return prev_area;
        }
    }
}