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.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        Point[] redList = new Point[n];
        for (int i = 0; i < n; i++) {
            int a = Integer.parseInt(sc.next());
            int b = Integer.parseInt(sc.next());
            redList[i] = new Point(a,b);
        }

        Point[] blueList = new Point[n];
        for (int i = 0; i < n; i++) {
            int a = Integer.parseInt(sc.next());
            int b = Integer.parseInt(sc.next());
            blueList[i] = new Point(a,b);
        }

        int ans = calc(redList, blueList);
        System.out.println(ans);

        sc.close();
    }

    static int calc(Point[] redList, Point[] blueList) {
//        System.out.println(redList);
        if (redList.length == 0) return 0;
        int[] result = new int[blueList.length+1]; // TODO

        Point redPoint = redList[redList.length-1];
        redList = Arrays.copyOf(redList, redList.length-1);
        for (int i = 0; i < blueList.length; i++) {
            if (redPoint.isGood(blueList[i])) {
                Point[] blueList2 = new Point[blueList.length-1];
                for (int j = 0; j < i; j++) {
                    blueList2[j] = blueList[j];
                }
                for (int j = i+1; j < blueList.length; j++) {
                    blueList2[j-1] = blueList[j];
                }
//                Point bluePoint = blueList2.remove(i);
//                System.out.println("[IN ]red:" + redPoint + " / blue:" + bluePoint);
                result[i] = 1 + calc(Arrays.copyOf(redList, redList.length), blueList2);
//                System.out.println("[OUT]red:" + redPoint + " / blue:" + bluePoint + ", result:" + result[i]);
            }
        }
//        result[blueList.size()] = calc(new ArrayList<>(redList), new ArrayList<>(blueList));
        result[blueList.length] = calc(redList, blueList);

        int max = 0;
        for (int i = 0; i <= blueList.length; i++) {
            if (max < result[i]) max = result[i];
        }

        return max;
    }

    static class Point {
        int x;
        int y;
        Point(int x, int y) {
            this.x = x;
            this.y = y;
        }

        boolean isGood(Point o) {
            return ((x < o.x) && (y < o.y));
        }

        @Override
        public String toString() {
            return "(" + x + "," + y + ")";
        }
    }

}