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[] a = new int[2 * N];
    int[] b = new int[2 * N];

    for (int i=0; i < N; i++) {
      int input = sc.nextInt();
      a[input] = sc.nextInt() + 1;
    }

    for (int i=0; i < N; i++) {
      int input = sc.nextInt();
      b[input] = sc.nextInt() + 1;
    }

    int count = 0;

    for (int i=0; i < 2*N; i++) {
      if (b[i] == 0) continue;

      int tmp_min = Integer.MAX_VALUE;
      int tmp_j = 2*N;
      boolean f = false;

      for (int j=i-1; j >= 0; j--){
        if (a[j] != 0) {
          if (b[i] - a[j] > 0 && b[i] - a[j] < tmp_min) {
            tmp_min = b[i] - a[j];
            tmp_j = j;
            f = true;
          }
        }
      }

      if (f) {
        a[tmp_j] = 0;
        count++;
        f = false;
      }
    }

    System.out.println(count);
  }
}