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[n];
    HashMap<Integer, Integer> map1 = new HashMap<Integer, Integer>();
    int[] c = new int[n];
    HashMap<Integer, Integer> map2 = new HashMap<Integer, Integer>();
    for(int i = 0; i < n; i++) {
      int b = sc.nextInt();
      a[i] = sc.nextInt();
      map1.put(a[i], b);
    }
    for(int i = 0; i < n; i++) {
      c[i] = sc.nextInt();
      int d = sc.nextInt();
      map2.put(c[i], d);
    }
    Arrays.sort(a);
    Arrays.sort(c);
    int[] used = new int[n];
    int ans = 0;
    for(int i = 0; i < n; i++) {
      for(int j = n - 1; j >= 0; j--) {
        if((c[i] > map1.get(a[j])) && (map2.get(c[i]) > a[j]) && (used[j] == 0)) {
          ans++;
          used[j] = 1;
          break;
        }
      }
    }
    System.out.println(ans);
  }
}