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.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        List<Grid> gridList = new ArrayList<>();

        int n = in.nextInt();
        for(int i = 0; i < n; i++) {
            gridList.add(new Grid(Color.RED, in.nextInt(), in.nextInt()));
        }
        for(int i = 0; i < n; i++) {
            gridList.add(new Grid(Color.BLUE, in.nextInt(), in.nextInt()));
        }
      
        gridList.sort(Comparator.comparing(Grid::getX).thenComparing(Grid::getColor));
        List<Grid> tmp = new ArrayList<>();
        int ans = 0;
        for (Grid grid : gridList) {
            if(grid.color == Color.RED) {
                tmp.add(grid);
            } else {
                List<Grid> list = tmp.stream()
                        .filter(g -> g.getY() < grid.getY())
                        .collect(Collectors.toList());
                if(list.size() > 0) {
                    ans++;
                    list.sort(Comparator.comparing(Grid::getY));
                    tmp.remove(list.get(list.size() - 1));
                }
            }
        }
        System.out.println(ans);
    }
}

class Grid {

    Color color;
    int x;
    int y;

    public Grid(Color color, int x, int y) {
        this.color = color;
        this.x = x;
        this.y = y;
    }
    public Color getColor() { return this.color; }
    public int getX() { return this.x; }
    public int getY() { return this.y; }

    public String toString(){
        return String.format(color + " \t" + x + ", " + y);
    }
}

enum Color {
    BLUE,
    RED
}