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();
		ArrayList<Point> reds = new ArrayList<Point>();
		for (int i = 0; i < n; i++) {
			reds.add(new Point(sc.nextInt(), sc.nextInt()));
		}
		ArrayList<Point> blues = new ArrayList<Point>();
		for (int i = 0; i < n; i++) {
			blues.add(new Point(sc.nextInt(), sc.nextInt()));
		}
		Collections.sort(reds, new Comparator<Point>(){
		public int compare(Point p1, Point p2){
			return p2.y - p1.y;
		}
		});
		Collections.sort(blues, new Comparator<Point>(){
		public int compare(Point p1, Point p2) {
			return p1.x - p2.x;
		}
		});
		int count = 0;
		for (Point b : blues) {
			Point x = null;
			for (Point r : reds) {
				if (r.isMatch(b)) {
					x = r;
					count++;
					break;
				}
			}
			if (x != null) {
				reds.remove(reds.indexOf(x));
			}
		}
		System.out.println(count);
		
	}
	
	public static class Point {
		public int x;
		public int y;
		
		public Point(int x, int y) {
			this.x = x;
			this.y = y;
		}
		
		public Point() {
			this(0, 0);
		}
		
		public boolean isMatch(Point p) {
			return (x < p.x && y < p.y);
		}
		
	}
}