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;
using System.Collections;
using System.Collections.Generic;
using System.Text;


class Program
{
    static void Main(string[] args)
    {
        // 入力
        //var s = Console.ReadLine();
        var n = int.Parse(Console.ReadLine());

        int[] a = new int[n];
        int[] b = new int[n];
        for (int i = 0; i < n; i++)
        {
            int[] tmp = Console.ReadLine().Split().Select(int.Parse).ToArray();
            a[i] = tmp[0];
            b[i] = tmp[1];
        }

        //y座標でソート
        Array.Sort(b, a);

        int[] c = new int[n];
        int[] d = new int[n];
        for (int i = 0; i < n; i++)
        {
            int[] tmp = Console.ReadLine().Split().Select(int.Parse).ToArray();
            c[i] = tmp[0];
            d[i] = tmp[1];
        }

        //x座標でソート
        Array.Sort(c, d);

        //青い点のうち最もx 座標が小さいものに注目します。この点と仲良しペアになれる点が存在した場合，そのような点のうち最も y 座標が大きいものと仲良しペアにしてよい
        int[][] jag = new int[n][];
        for (int i = 0; i < jag.Length; i++)
        {
            jag[i] = new int[n];
        }

        //i が青い点、kが赤い点
        var hset = new HashSet<int>();
        for (int i = 0; i < n; i++)
        {
            for (int k = n - 1; k >= 0; k--)
            {
                if (hset.Contains(k)) continue;

                if (a[k] < c[i] && b[k] < d[i])
                {
                    jag[i][k] = 1;
                    hset.Add(k);
                    break;
                }
            }
        }

        var ans = 0;
        for (int i = 0; i < n; i++)
        {
            int sum = jag[i].Sum();
            if (sum != 0)
            {
                ans++;
            }
        }

        // 出力
        Console.WriteLine(ans);
    }
}