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.*;

public class Main {

    private final static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    private final static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

    private static class Point {
        public int x, y;
        public char color;

        public Point(int x, int y, char color){
            this.x = x;
            this.y = y;
            this.color = color;
        }
    };

    public static void main(String[] args) throws IOException {

        int N = Integer.parseInt(br.readLine());
        List<Point> arr = new ArrayList<>();

        for(int i = 0; i < N; i++) {
            StringTokenizer st = new StringTokenizer(br.readLine(), " ");
            int a = Integer.parseInt(st.nextToken());
            int b = Integer.parseInt(st.nextToken());
            Point p = new Point(a, b, 'r');
            arr.add(p);
        }

        for(int i = 0; i < N; i++){
            StringTokenizer st = new StringTokenizer(br.readLine(), " ");
            int a = Integer.parseInt(st.nextToken());
            int b = Integer.parseInt(st.nextToken());
            Point p = new Point(a, b, 'b');
            arr.add(p);
        }

        arr.sort((Point o1, Point o2) -> {
            if(o1.x != o2.x){
                return Integer.compare(o1.x, o2.x);
            }
            if(o1.y != o2.y){
                return Integer.compare(o1.y, o2.y);
            }
            return 0;
        });

        int answer = 0;
        List<Point> reds = new ArrayList<>();
        for(Point p : arr){
            if(p.color == 'b'){
                Point maximumYRed = null;
                for(Point red : reds){
                    if(red.y < p.y && (maximumYRed == null || maximumYRed.y < red.y)){
                        maximumYRed = red;
                    }
                }

                if(maximumYRed != null) {
                    answer += 1;
                    reds.remove(maximumYRed);
                }
            }else{
                reds.add(p);
            }
        }

        bw.write(String.format("%d\n", answer));
        bw.flush();
    }
}