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;
using System.Linq;

namespace Program
{
    public class BluePoint
    {
        internal int x;
        internal int y;
        
        public BluePoint()
        {
            x = 0;
            y = 0;
        }
    }
    
    public class RedPoint
    {
        internal int x;
        internal int y;
        
        public RedPoint()
        {
            x = 0;
            y = 0;
        }
    }
    public class Program
    {	
        public static void Main()
    	{
            int N = int.Parse(Console.ReadLine());

            BluePoint[] BP = new BluePoint[N];
            RedPoint[] RP = new RedPoint[N];
            for(int i = 0 ; i < N ; i++)
            {
                BP[i] = new BluePoint();
                RP[i] = new RedPoint();
            }
            
            List<string> list = new List<string>();
            for(int i = 0 ; i < N ; i++)
            {
                list.Add(Console.ReadLine());
            }
            list.Sort();
            
            int[] n; 
            for(int i = 0 ; i < N ; i++)
            {
                n = list[i].Split(' ').Select(s => int.Parse(s)).ToArray();
                BP[i].x = n[0];
                BP[i].y = n[1];
            }
            
            List<string> list2 = new List<string>();
            for(int i = 0 ; i < N ; i++)
            {
                list2.Add(Console.ReadLine());
            }
            list2.Sort();
            
            for(int i = 0 ; i < N ; i++)
            {
                n = list2[i].Split(' ').Select(s => int.Parse(s)).ToArray();
                RP[i].x = n[0];
                RP[i].y = n[1];
            }
            
            int cnt = 0;
            int index;
            bool set;
            for(int i = 0 ; i < N ; i++)
            {
                set = true; 
                index = 0;
                for(int j = N-1 ; j >= 0 ; j--)
                {
                    if(RP[i].x >= BP[j].x && RP[i].y >= BP[j].y && set)
                    {
                        BP[j].x = 99999999;
                        BP[j].y = 99999999;
                        cnt++;
                        set = false;
                    }
                } 
            }
            
            Console.WriteLine(cnt);
    	}
    }
}