Problem:
Score : 400 points

Problem Statement

On a two-dimensional plane, there are N red points and N blue points.
The coordinates of the i-th red point are (a_i, b_i), and the coordinates of the i-th blue point are (c_i, d_i).

A red point and a blue point can form a friendly pair when, the x-coordinate of the red point is smaller than that of the blue point, and the y-coordinate of the red point is also smaller than that of the blue point.

At most how many friendly pairs can you form? Note that a point cannot belong to multiple pairs.

Constraints

All input values are integers.

1 \leq N \leq 100

0 \leq a_i, b_i, c_i, d_i < 2N

a_1, a_2, ..., a_N, c_1, c_2, ..., c_N are all different.

b_1, b_2, ..., b_N, d_1, d_2, ..., d_N are all different.

Input

Input is given from Standard Input in the following format:

N
a_1 b_1
a_2 b_2
:
a_N b_N
c_1 d_1
c_2 d_2
:
c_N d_N

Output

Print the maximum number of friendly pairs.

Sample Input 1

3
2 0
3 1
1 3
4 2
0 4
5 5

Sample Output 1

2

For example, you can pair (2, 0) and (4, 2), then (3, 1) and (5, 5).

Sample Input 2

3
0 0
1 1
5 2
2 3
3 4
4 5

Sample Output 2

2

For example, you can pair (0, 0) and (2, 3), then (1, 1) and (3, 4).

Sample Input 3

2
2 2
3 3
0 0
1 1

Sample Output 3

0

It is possible that no pair can be formed.

Sample Input 4

5
0 0
7 3
2 2
4 8
1 6
8 5
6 9
5 4
9 1
3 7

Sample Output 4

5

Sample Input 5

5
0 0
1 1
5 5
6 6
7 7
2 2
3 3
4 4
8 8
9 9

Sample Output 5

4

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        List<Point> red = new ArrayList<>();
        List<Point> blue = new ArrayList<>();

        for (int i=0; i<N; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();

            red.add(new Point(a, b));
        }
        for (int i=0; i<N; i++) {
            int c = sc.nextInt();
            int d = sc.nextInt();

            blue.add(new Point(c, d));
        }

        System.out.println(solve(N, red, blue));

    }

    static class Point {
        public int x, y;

        Point(int x, int y) {
            this.x = x;
            this.y = y;
        }
    }

    private static int solve(int N, List<Point> red, List<Point> blue) {
        int ans = 0;

        Collections.sort(red, new Comparator<Point>() {
            public int compare(Point p1, Point p2) {
                return p1.x - p2.x;
            }
        });
        Collections.sort(blue, new Comparator<Point>() {
            public int compare(Point p1, Point p2) {
                return p1.x - p2.x;
            }
        });

        for (int i=0; i<blue.size(); i++) {
            Iterator it = red.iterator();
            Point max = null;
            while (it.hasNext()) {
                Point p = (Point)it.next();
                if (p.x < blue.get(i).x && p.y < blue.get(i).y) {
//                    System.err.println(p.x + ", " + p.y + " < " + blue.get(i).x + ", " + blue.get(i).y);
                    if (max == null || max.y < p.y) {
                        max = p;
                    }

                }
            }
            if (max != null) {
                ans++;
                red.remove(max);
            }
        }

        return ans;
    }
}