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;

namespace AtCorder
{
	public class Program
	{
		static void Main(string[] args)
		{
			int n = int.Parse(Console.ReadLine());
			var reds = new Tuple<int, int>[n];
			var blues = new Tuple<int, int>[n];
			for (int i = 0; i < n; i++) {
				var ab = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
				reds[i] = new Tuple<int, int>(ab[0], ab[1]);
			}

			for (int i = 0; i < n; i++) {
				var ab = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
				blues[i] = new Tuple<int, int>(ab[0], ab[1]);
			}

			List<int>[] blueTargets = new List<int>[n];
			for (int i = 0; i < n; i++) {
				blueTargets[i] = new List<int>();
				for (int j = 0; j < n; j++) {
					if (reds[i].Item1 < blues[j].Item1 && reds[i].Item2 < blues[j].Item2) {
						blueTargets[i].Add(j);
					}
				}
			}

			var targets = blueTargets.OrderBy(x => x.Count()).ToArray();

			int ans = 0;
			bool[] uses = new bool[n];
			foreach (var target in targets) {
				foreach (int index in target) {
					if (uses[index] == false) {
						uses[index] = true;
						++ans;
						break;
					}
				}
			}

			Console.WriteLine(ans);
		}
	}
}