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.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using static System.Console;

namespace arc91
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(ReadLine());

            var a = new int[n];
            var b = new int[n];
            var c = new int[n];
            var d = new int[n];

            for (int i = 0; i < n; i++)
            {
                var s = ReadLine().Split(' ');
                a[i] = int.Parse(s[0]);
                b[i] = int.Parse(s[0]);

            }
            for (int i = 0; i < n; i++)
            {
                var s = ReadLine().Split(' ');
                c[i] = int.Parse(s[0]);
                d[i] = int.Parse(s[0]);
            }

           
            int count = 0;
            var removed = new List<int>();
            var candidate = new List<int>();
            for (int i = 0; i < n; i++)
            {
                candidate.Clear();
                for (int j = 0; j < n; j++)
                {
                    if (a[j] < c[i] && b[j] < d[i] && !removed.Contains(j))
                    {
                        candidate.Add(j);
                    }
                }
                if (candidate.Count > 0)
                {
                    int max_yi = candidate[0];
                    foreach (var can in candidate)
                    {
                        if (b[can] > b[max_yi])
                        {
                            max_yi = can;
                        }
                    }
                    removed.Add(max_yi);
                    count++;
                }
            }
            WriteLine(count);

        }
    }
}