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: Accepted)

    using System;
    using System.Text;
    using System.Linq;
    using System.Collections;
    using System.Collections.Generic;
    using static System.Console;
    using static System.Math;
     
    namespace NotFounds
    {
        public class Program
        {
            public static void Main(string[] args)
            {
                var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
                Console.SetOut(sw);
                new Program().Solve(new ConsoleInput(Console.In, ' '));
                Console.Out.Flush();
            }
     
            public void Solve(ConsoleInput cin)
            {
                checked
                {
	        var N = cin.ReadInt;
	        var red = new List<Point>();
	        var blue = new List<Point>();
	        for (int i = 0; i < N; ++i)
		red.Add(new Point(cin.ReadInt, cin.ReadInt));        
		
	        for (int i = 0; i < N; ++i)
		blue.Add(new Point(cin.ReadInt, cin.ReadInt));
		
	        var r = red.OrderByDescending(p => p.y).ThenByDescending(p => p.x).ToArray();
	        var b = blue.OrderBy(p => p.x).ThenBy(p => p.y).ToArray();
	        
	        var used = new bool[N];
	        var cnt = 0;
	        for (int i = 0; i < N; ++i)
	        {
	        	for (int j = 0; j < N; ++j)
	        	{
	        	    if (r[i].x < b[j].x && r[i].y < b[j].y && !used[j])
		    {
		        cnt++;
		        used[j] = true;
		        break;
		    }
	        	}
	        }
	        
	        WriteLine(cnt);
                }
            }
        }
        
        public struct Point
        {
        	public int x;
        	public int y;
        	public Point(int _x, int _y) { x = _x; y = _y; }
        }
     
        public class ConsoleInput
        {
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;
            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }
            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }
            public string ReadLine { get { return _stream.ReadLine(); }}
            public int ReadInt { get { return int.Parse(Read); }}
            public long ReadLong { get { return long.Parse(Read); }}
            public double ReadDouble { get { return double.Parse(Read); }}
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret;}
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret;}
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret;}
            public void ReadIntArrays(long N, out int[] A, out int[] B) { A = new int[N]; B = new int[N]; for (long i = 0; i < N; ++i) { A[i] = ReadInt; B[i] = ReadInt; }}
            public void ReadIntArrays(long N, out int[] A, out int[] B, out int[] C) { A = new int[N]; B = new int[N]; C = new int[N]; for (long i = 0; i < N; ++i) { A[i] = ReadInt; B[i] = ReadInt; C[i] = ReadInt; }}
            public void ReadLongArrays(long N, out long[] A, out long[] B) { A = new long[N]; B = new long[N]; for (long i = 0; i < N; ++i) { A[i] = ReadLong; B[i] = ReadLong; }}
        }
    }