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: Wrong Answer)

import java.awt.Point;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		try (Scanner scanner = new Scanner(System.in)) {
			int count = scanner.nextInt();
			List<Point> redList = new ArrayList<>(count);
			for (int i = 0; i < count; i++) {
				int x = scanner.nextInt();
				int y = scanner.nextInt();
				redList.add(new java.awt.Point(x, y));
			}

			List<Point> blueList = new ArrayList<>(count);
			for (int i = 0; i < count; i++) {
				int x = scanner.nextInt();
				int y = scanner.nextInt();
				blueList.add(new java.awt.Point(x, y));
			}

			C c = new C();
			Collections.sort(redList, c);
			Collections.sort(blueList, c);

			int result = 0;
			for (int i = redList.size() - 1; i >= 0; i--) {
				int index = check(redList.get(i), blueList);
				if (index >= 0) {
					result++;
					blueList.remove(index);
				}
			}

			System.out.println(result);
		}
	}

	private static int check(Point red, List<Point> blueList) {
		for (int i = blueList.size() - 1; i >= 0; i--) {
			Point blue = blueList.get(i);
			if (red.x < blue.x && red.y < blue.y) {
				return i;
			}
		}

		return -1;
	}

	private static class C implements Comparator<Point> {
		@Override
		public int compare(Point o1, Point o2) {
			int o1High = 0;
			int o1Low = 0;
			if (o1.x > o1.y) {
				o1High = o1.x;
				o1Low = o1.y;
			} else {
				o1High = o1.y;
				o1Low = o1.x;
			}

			int o2High = 0;
			int o2Low = 0;
			if (o2.x > o2.y) {
				o2High = o2.x;
				o2Low = o2.y;
			} else {
				o2High = o2.y;
				o2Low = o2.x;
			}

			if (o1High > o2High) {
				return 1;
			} else if (o1High < o2High) {
				return -1;
			}

			return o1Low - o2Low;
		}
	}
}