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 ConsoleApp1
{
	class Program
	{
		static void Main(string[] a_asArgs)
		{
			int l_iN = int.Parse(Console.ReadLine());

			List<Point> l_lpRed = new List<Point>();
			List<Point> l_lpBlue = new List<Point>();
			List<Point> l_lpBlue2 = new List<Point>();

			for (int l_iIndex = 0; l_iIndex < l_iN; l_iIndex++)
			{
				int[] l_aiXY = Console.ReadLine().Split(' ').Select(a => int.Parse(a)).ToArray();
				l_lpRed.Add(new Point { X= l_aiXY[0], Y = l_aiXY[1] });
			}
			for (int l_iIndex = 0; l_iIndex < l_iN; l_iIndex++)
			{
				int[] l_aiXY = Console.ReadLine().Split(' ').Select(a => int.Parse(a)).ToArray();
				l_lpBlue.Add(new Point { X = l_aiXY[0], Y = l_aiXY[1] });
				l_lpBlue2.Add(new Point { X = l_aiXY[0], Y = l_aiXY[1] });
			}
			l_lpRed.Sort(new PointComparer());
			l_lpBlue.Sort(new PointComparer());

			int l_iCount = 0;
			foreach (Point l_pRed in l_lpRed)
			{
				foreach (Point l_pBlue in l_lpBlue)
				{
					if (l_pRed.X < l_pBlue.X && l_pRed.Y < l_pBlue.Y)
					{
						l_lpBlue.Remove(l_pBlue);
						l_iCount++;
						break;
					}
				}
			}

			l_lpRed.Sort(new PointComparer2());
			l_lpBlue2.Sort(new PointComparer2());

			int l_iCount2 = 0;
			foreach (Point l_pRed in l_lpRed)
			{
				foreach (Point l_pBlue in l_lpBlue2)
				{
					if (l_pRed.X < l_pBlue.X && l_pRed.Y < l_pBlue.Y)
					{
						l_lpBlue2.Remove(l_pBlue);
						l_iCount2++;
						break;
					}
				}
			}

			Console.WriteLine(l_iCount > l_iCount2 ? l_iCount : l_iCount2);
		}

		private struct Point
		{
			public int X;
			public int Y;
		}

		private class PointComparer : IComparer<Point>
		{
			public int Compare(Point a_Point1, Point a_Point2)
			{
				if (a_Point1.X == a_Point2.X)
				{
					return a_Point1.Y - a_Point2.Y;
				}
				else
				{
					return a_Point1.X - a_Point2.X;
				}
			}
		}
		private class PointComparer2 : IComparer<Point>
		{
			public int Compare(Point a_Point1, Point a_Point2)
			{
				if (a_Point1.Y == a_Point2.Y)
				{
					return a_Point1.X - a_Point2.X;
				}
				else
				{
					return a_Point1.Y - a_Point2.Y;
				}
			}
		}
	}
}