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;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Linq;
using static System.Console;
using static System.Math;

namespace abc_91_c
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(ReadLine());

            int[][] red = new int[n][];
            int[][] blue = new int[n][];

            for(int i = 0; i<n; i++)
            {
                int[] input = ReadLine().Split().Select(int.Parse).ToArray();
                red[i] = input;
            }

            for(int i = 0; i<n; i++)
            {
                int[] input = ReadLine().Split().Select(int.Parse).ToArray();
                blue[i] = input;
            }

            red = red.OrderByDescending(a => a[1]).ToArray();
            blue = blue.OrderBy(a => a[0]).ToArray();
            int count=0;

            for(int i=0; i<n; i++)
            {
                for(int j=0; j<n; j++)
                {
                   if(red[j] == null) continue;
                   if(red[j][0] < blue[i][0] && red[j][1] < blue[i][1])
                   {
                       count++;
                       red[j] = null;
                       break;
                   }
                }
            }
            WriteLine(count);
        }
    }
}