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.awt.Point;
import java.util.Iterator;
import java.util.Scanner;
import java.util.TreeSet;

public class Main {
	public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		TreeSet<KUSO> ts = new TreeSet<>();
		for(int i = 0; i < n; i++) {
			ts.add(new KUSO(new Point(sc.nextInt(),sc.nextInt()), true));
		}
		for(int i = 0; i < n; i++) {
			ts.add(new KUSO(new Point(sc.nextInt(),sc.nextInt()), false));
		}
		Iterator<KUSO> itr = ts.iterator();
		TreeSet<Integer> treeone = new TreeSet<>();
		long count = 0;
		while(itr.hasNext()) {
			KUSO k = itr.next();
			if(k.isRed) {
				treeone.add(k.p.y);
			} else {
				Integer i = treeone.floor(k.p.y);
				if(i!=null) {
					count++;
					treeone.remove(i);
				}
			}
		}
		System.out.println(count);
	}
}
class KUSO implements Comparable<KUSO>{
	Point p;
	boolean isRed;
	KUSO(Point p, boolean b) {
		this.p = p;
		this.isRed = b;
	}
	@Override
	public int compareTo(KUSO o) {
		return Integer.compare(this.p.x, o.p.x);
	}
	@Override
	public boolean equals(Object obj) {
		if(obj instanceof KUSO) {
			KUSO kuso = (KUSO) obj;
			if(kuso.p.equals(this.p)&&kuso.isRed==this.isRed) {
				return true;
			}
		}
		return false;
	}
}