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.Linq;
using System.Collections.Generic;

namespace Algorithm
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var red = new int[N][];
            var blue = new int[N][];

            for (var i = 0; i < N; i++)
                red[i] = Console.ReadLine().Split().Select(int.Parse).ToArray();
            for (var i = 0; i < N; i++)
                blue[i] = Console.ReadLine().Split().Select(int.Parse).ToArray();

            red = red.OrderBy(z => z[0]).ThenBy(x => x[1]).ToArray();

            var useRed = new bool[N];
            var useBlue = new bool[N];
            var total = 0;
            for (var i = 0; i < N; i++)
            {
                var min = int.MaxValue;
                var minInd = int.MaxValue;
                if (useRed[i]) continue;
                for (var j = 0; j < N; j++)
                {
                    if (useBlue[j]) continue;
                    if (red[i][0] < blue[j][0] && red[i][1] < blue[j][1])
                    {
                        if (blue[j][0] - red[i][0] < min)
                        {
                            min = blue[j][0] - red[i][0];
                            minInd = j;
                        }
                        if (blue[j][1] - red[i][1] < min)
                        {
                            min = blue[j][1] - red[i][1];
                            minInd = j;
                        }
                    }
                }
                if (min != int.MaxValue)
                {
                    useRed[i] = true;
                    useBlue[minInd] = true;
                    total++;
                }
            }
            Console.WriteLine(total);
        }
    }
}