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;

public class Test
{
	public static void Main()
	{
		// your code goes here
		int count = 0, n = int.Parse(Console.ReadLine());
		int[,] red = new int[n,2];
		int[,] blue = new int[n,2];
		bool[] check = new bool[n];
		red = Read(n);
		blue = Read(n);
		red = Sort(n, red);
		blue = Sort(n, blue);
		
		for(int i=0;i<n;i++)
		{
			int a=0, b=0, j;
			for(j=0;j<n;j++)
			{
				if(check[j]==false&&red[i,0]<blue[j,0])
				{
					count++;
					a = blue[j,1];
					b = j;
					break;
				}
			}
			if(j<n)
			{
				for(j++;j<n;j++)
				{
					if(check[j]==false&&a<blue[j,1])
					{
						a = blue[j,1];
						b = j;
					}
				}
				check[b] = true;
			}
		}
		Console.WriteLine(count);
	}
	public static int[,] Read(int n)
	{
		int[,] point = new int[n,2];
		for(int i=0;i<n;i++)
		{
			string[] line = Console.ReadLine().Split(' ');
			point[i,0] = int.Parse(line[0]);
			point[i,1] = int.Parse(line[1]);
		}
		return point;
	}
	public static int[,] Sort(int n, int[,] point)
	{
		for(int i=0;i<n;i++)
		{
			for(int j=i+1;j<n;j++)
			{
				if(point[i,0]>point[j,0])
				{
					int a = point[i,0], b = point[i,1];
					point[i,0] = point[j,0];
					point[i,1] = point[j,1];
					point[j,0] = a;
					point[j,1] = b;
				}
			}
		}
		return point;
	}
}