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.*;

class Point implements Comparable<Point>{
    public int x,y;
    public int color;
    public static int red=0,
                      blue=1;
    
    public Point(int x, int y, int color){
    	this.x=x;
    	this.y=y;
    	this.color=color;
    }
    
    public int compareTo(Point another){
    	return this.x-another.x;
    }
    
    public boolean connectable(Point another){
    	return (this.x<another.x && this.y<another.y && this.color==red && another.color==blue)
    	     ||(this.x>another.x && this.y>another.y && this.color==blue && another.color==red);
    }
    
    public void use(){
    	color = -1;
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        Point[] r = new Point[N];
        for(int n=0;n<N;n++) r[n]= new Point(sc.nextInt(), sc.nextInt(), 0);
        Point[] b = new Point[N];
        for(int n=0;n<N;n++) b[n]= new Point(sc.nextInt(), sc.nextInt(), 1);
        Arrays.sort(r);
        Arrays.sort(b);
        
        int ans=0;
        
        for(Point blue:b){
        	int highest = -1;
        	for(Point red:r) if(blue.connectable(red) && red.y>highest)  highest=red.y;
        	if(highest>=0){
        	    ans++;
        	    for(Point red:r)if(red.y==highest) red.use();
        	}
        }
        
        System.out.println(ans);
        
        
        
        
    }
}