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;

namespace Problem_B
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var red = new List<Tuple<int, int>>();
            var blue = new List<Tuple<int, int>>();
            for (var i = 0; i < n; i++)
            {
                var p = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
                red.Add(Tuple.Create(p[0], p[1]));
            }
            for (var i = 0; i < n; i++)
            {
                var p = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
                blue.Add(Tuple.Create(p[0], p[1]));
            }

            red.Sort();
            blue.Sort((t1, t2) => t1.Item2 == t2.Item2 ? 0 : (t1.Item2 < t2.Item2 ? -1 : 1));
            var count = 0;
            for (var i = 0; i < n; i++)
            {
                for (var j = 0; j < n; j++)
                {
                    if (blue[j] != null && red[i].Item1 < blue[j].Item1 && red[i].Item2 < blue[j].Item2)
                    {
                        count++;
                        blue[j] = null;
                        break;
                    }
                }
            }
            Console.WriteLine($"{count}");
        }
    }
}