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.Collections.Generic;
using System.Linq;

class Program
{
    //static void Main_o(string[] args)
    //{
    //    // 整数の入力
    //    int a = int.Parse(Console.ReadLine());
    //    // スペース区切りの整数の入力
    //    while (a-- > 0)
    //    {
    //        Console.WriteLine("a");
    //    }
    //    string[] input = Console.ReadLine().Split(' ');
    //    int b = int.Parse(input[0]);
    //    int c = int.Parse(input[1]);
    //    // 文字列の入力
    //    string s = Console.ReadLine();
    //    //出力
    //    Console.WriteLine((a + b + c) + " " + s);

    //}

    //static void Main(string[] args)
    //{
    //    // 整数の入力
    //    string[] input = Console.ReadLine().Split(' ');
    //    int b = int.Parse(input[0]);
    //    int c = int.Parse(input[1]);
    //    int a = int.Parse(input[2]);
    //    //出力
    //    Console.WriteLine( (b+c < a ? "No" : "yes" ) );
    //    Console.ReadLine();
    //}

    static void Main(string[] args)
    {
        // 整数の入力
        int n = int.Parse(Console.ReadLine());
        int[] xtoy_r = new int[2*n];
        int[] ytox_b = new int[2 * n];

        int i = 2*n;
        while(i-- > 0)
        {
            xtoy_r[i] = int.MaxValue;
            ytox_b[i] = int.MinValue;
        }

        i = n;
        while (i-- > 0)
        {
            string[] input = Console.ReadLine().Split(' ');
            //b[int.Parse(input[0]), int.Parse(input[1])] = true;
            xtoy_r[int.Parse(input[0])] = int.Parse(input[1]);
        }
        i = n;
        while (i-- > 0)
        {
            string[] input = Console.ReadLine().Split(' ');
            //b[int.Parse(input[0]), int.Parse(input[1])] = true;
            ytox_b[int.Parse(input[1])] = int.Parse(input[0]);
        }

        i = 0;
        int cnt = 0;
        
        while (i < 2*n)
        {
            if (ytox_b[i] > 0)
            {
                int x = ytox_b[i];
                while (x-- > 0)
                {
                    if (xtoy_r[x] < i)
                    {
                        cnt++;
                        xtoy_r[x] = int.MaxValue;
                        break;
                    }
                }
            }
            i++;
        }
        
        Console.WriteLine ( cnt );
    }
}