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) {
		new Main().execute();
	}

	public void execute() {
		Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		Point[] red = new Point[N];
		Point[] blue = new Point[N];

		for (int i = 0; i < N; i++) {
			int x = sc.nextInt();
			int y = sc.nextInt();
			red[i] = new Point(x, y);
		}

		for (int i = 0; i < N; i++) {
			int x = sc.nextInt();
			int y = sc.nextInt();
			blue[i] = new Point(x, y);
		}

		Comparator<Point> cmp = new Comparator<Main.Point>() {
			@Override
			public int compare(Point o1, Point o2) {
				// TODO Auto-generated method stub
				if (o1.x == o2.x) {
					return o1.y - o2.y;
				} else {
					return o1.x - o2.x;
				}
			}
		};

		Arrays.sort(red, cmp);
		Arrays.sort(blue, cmp);
		boolean[] matched = new boolean[N];
		int pairs = 0;

		for (int i = 0; i < N; i++) {
			int bx = blue[i].x;
			int j = 0;
			int my = -1;
			int k = -1;
			while (j < red.length && red[j].x < bx) {
				if (!matched[j] && matchable(red[j], blue[i]) && my < red[j].y) {
					my = red[j].y;
					k = j;
				}
				j++;
			}
			if (k >= 0) {
				pairs += 1;
				matched[k] = true;
			}
		}
		System.out.println(pairs);

		sc.close();

	}

	private boolean matchable(Point r, Point b) {
		return (r.x < b.x) && (r.y < b.y);
	}

	class Point {
		public final int x;
		public final int y;

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

}