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: Accepted)

using System;
using System.Linq;//リストの使用
using System.Collections.Generic;
class Program
{
	static void Main()
	{
    long answer = 0;
		long n = long.Parse(Console.ReadLine());//int.Parseは文字列を整数に変換。
    long[][] vertexesRed = new long[n][];//x座標、y座標、使ったら1
    long[][] vertexesBlue = new long[n][];//x座標、y座標、使ったら1
    for(long i = 0; i < n; i++)
    {
      vertexesRed[i] = new long[3];
      vertexesBlue[i] = new long[2];
    }
    for(long i = 0; i < n; i++)
    {
      long[] nums = Array.ConvertAll(Console.ReadLine().Split(' '),long.Parse);
      vertexesRed[i][0] = nums[0];
      vertexesRed[i][1] = nums[1];
    }
    for(long i = 0; i < n; i++)
    {
      long[] nums = Array.ConvertAll(Console.ReadLine().Split(' '),long.Parse);
      vertexesBlue[i][0] = nums[0];
      vertexesBlue[i][1] = nums[1];
    }
    Array.Sort(vertexesRed, (a, b) => a[0].CompareTo(b[0]));//x座標でソート
    Array.Sort(vertexesBlue, (a, b) => a[0].CompareTo(b[0]));

    long[] maxMemo = new long[2];//番号とy座標

    for(long blueNum = 0; blueNum < n; blueNum++)
    {
    maxMemo[0] = -1;
    maxMemo[1] = -1;
      for(long redNum = 0; redNum < n; redNum++)
      {
        if(vertexesRed[redNum][0] < vertexesBlue[blueNum][0] &&
          vertexesRed[redNum][1] < vertexesBlue[blueNum][1] &&
          vertexesRed[redNum][1] > maxMemo[1] &&
          vertexesRed[redNum][2] == 0)
        {
          maxMemo[1] = vertexesRed[redNum][1];
          maxMemo[0] = redNum;
        }
      }
      //Console.WriteLine(maxMemo[0]+" "+maxMemo[1]);
      
      if(maxMemo[0] != -1)
      {
        vertexesRed[maxMemo[0]][2] = 1;
        answer++;
        //Console.WriteLine(maxMemo[0]+" "+maxMemo[1]);
      }
      
    }

		Console.WriteLine(answer);//WriteLineをWriteとすると、改行なしで出力。
	}
}