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: Time Limit Exceeded)

import java.util.*;
	public class Main{
        public static void main(String[] args){
            Scanner sc = new Scanner(System.in);
            //入力
            int n = Integer.parseInt(sc.next());

            int[][] red = new int [n][2];
            int[][] blue = new int [n][2];
            
            for(int i=0; i<n; i++){
            	red[i][0] = Integer.parseInt(sc.next());
            	red[i][1] = Integer.parseInt(sc.next());
            }
            for(int i=0; i<n; i++){
            	blue[i][0] = Integer.parseInt(sc.next());
            	blue[i][1] = Integer.parseInt(sc.next());
            }
            
            //出力
            System.out.println(calc(red, blue, n));
            sc.close();
        }
        
        public static int calc(int[][] red, int[][] blue, int n){
        	int ret = 0;
        	int temp0 = 0, temp1=0;
        	
        	if(n==0){
        		return 0;
        	}
        	
        	for(int i=0; i<n; i++){
        		for(int j=0; j<n; j++){
        			if(red[i][0] < blue[j][0] && red[i][1] < blue[j][1]){
        				temp0 = red[n-1][0];
        				temp1 = red[n-1][1];
        				red[n-1][0] = red[i][0];
        				red[n-1][1] = red[i][1];
        				red[i][0] = temp0;
        				red[i][1] = temp1;
        				
        				temp0 = blue[n-1][0];
        				temp1 = blue[n-1][1];
        				blue[n-1][0] = blue[j][0];
        				blue[n-1][1] = blue[j][1];
        				blue[j][0] = temp0;
        				blue[j][1] = temp1;
        				
        				if(ret < 1 + calc(red, blue, n-1)){
        					ret = 1 + calc(red, blue, n-1);
        				}
        			}
        		}
        	}
        	
            return ret;
        }
    }