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.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[][] r = new int[n][2];
        int[][] b = new int[n][2];
        boolean[] buse = new boolean[n];
        for(int i=0; i<n; i++){
            r[i][0] = sc.nextInt();
            r[i][1] = sc.nextInt();            
        }
        for(int i=0; i<n; i++){
            b[i][0] = sc.nextInt();
            b[i][1] = sc.nextInt();       
            buse[i] = false;
        }
        sc.close();

        int ans = 0;

        MyComp comp = new MyComp();
        Arrays.sort(r, comp);

        for(int i=0; i<n; i++){
            int rx = r[n-i-1][0];
            int ry = r[n-i-1][1];
            int bymin = 1000;
            int byminpos = 0;
            for(int j=0; j<n; j++){
                if(b[j][0] > rx && b[j][1] > ry && b[j][1] < bymin && !buse[j]){
                    bymin = b[j][1];
                    byminpos = j;
                }
            }
            if(bymin != 1000){
                ans++;
                buse[byminpos] = true;
            }
        }

        System.out.println(ans);
    }
}

class MyComp implements Comparator{
    @Override
    public int compare(Object i1, Object i2){
        return ((int[])i1)[0] - ((int[])i2)[0];
    }
}