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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections;
using System.Collections.Generic;
class Program
{
  static void Main(string[] args)
  {
    int[] rx = new int[110];
    int[] ry = new int[110];
    int[] bx = new int[110];
    int[] by = new int[110];
    // スペース区切りの整数の入力

    int N = int.Parse(Console.ReadLine());
    for (int i = 0; i < N; i++) {
      string[] input = Console.ReadLine().Split(' ');
      rx[i] = int.Parse(input[0]);
      ry[i] = int.Parse(input[0]);
    }
    for (int i = 0; i < N; i++) {
      string[] input = Console.ReadLine().Split(' ');
      bx[i] = int.Parse(input[0]);
      by[i] = int.Parse(input[0]);
    }

    int[,] table = new int[110, 110];
    int lastvalue = 0;
    IDictionary<string, bool> map = new Dictionary<string, bool>();

    for (int i = 0; i < N * N; i++) {
      string fp = "";
      bool firstchk = false;
      int count = 0;
      bool[] chk = new bool[110];
      for (int j = 0; j < N; j++) {
        for (int t = 0; t < N; t++) {
          if (rx[j] < bx[t] && ry[j] < by[t] && chk[t] == false) {
            string pair = ""+j+","+t;
            if (!map.ContainsKey(pair)) {
              chk[t] = true;
              count++;
              if (firstchk == false) {
                firstchk = true;
                fp = pair;
              }
              break;
            }
          }
        }

      }
      if (lastvalue < count)lastvalue = count;
      if (fp=="")break;
      map.Add(fp, true);
    }

    Console.WriteLine(lastvalue);


  }
}