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.*;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.util.Arrays;
import java.util.List;
import java.util.ArrayList;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Collections;
import java.awt.Point;


public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        List<Point> blue = new ArrayList();
        List<Point> red = new ArrayList();
        
        for (int i = 0; i < n; i++) {
            String[] xy = br.readLine().split(" ");
            int x = Integer.parseInt(xy[0]);
            int y = Integer.parseInt(xy[1]);
            red.add(new Point(x, y));
        }
        
        for (int i = 0; i < n; i++) {
            String[] xy = br.readLine().split(" ");
            int x = Integer.parseInt(xy[0]);
            int y = Integer.parseInt(xy[1]);
            blue.add(new Point(x, y));
        }
        
        Collections.sort(blue, new Comparator<Point>() {
            @Override
            public int compare(Point p1, Point p2) {
                return p1.x - p2.x;
            }
        });
        
        Collections.sort(red, new Comparator<Point>() {
            @Override
            public int compare(Point p1, Point p2) {
                return p1.x - p2.x;
            }
        });
        
        int max_y = -1;
        int r_ind = -1;
        int count = 0;
        boolean matched = false;
        for (int i = 0; i < blue.size(); i++) {
            Point b = blue.get(i);
            for (int j = 0; j < red.size(); j++) {
                Point r = red.get(j);
                if ((b.x - r.x > 0) && (b.y - r.y > 0)) {
                    if (r.y > max_y) {
                        //System.out.println("aaa");
                        max_y = r.y;
                        r_ind = j;
                        matched = true;
                    }
                }
            }
            if (matched) {
                //blue.remove(i);
                red.remove(r_ind);
                count++;
            }
            else {
                //blue.remove(i);
            }
            matched = false;
            max_y = -1;
        }
        
        System.out.println(count);
    }
}

class Box {
    int w;
    int h;
    public Box(int w, int h) {
        this.w = w;
        this.h = h;
    }
}

class BoxComparator1 implements Comparator<Box>{
	public int compare(Box b1, Box b2) {
		return b1.w - b2.w;
	}
}

class BoxComparator2 implements Comparator<Box> {
    public int compare(Box b1, Box b2) {
        return b1.h - b2.h;
    }
}