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.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace C
{
    public class Program
    {
        static void Main(string[] args)
        {
            var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            Solve();
            Console.Out.Flush();
        }

        public static void Solve()
        {
            var N = int.Parse(Console.ReadLine());
            var abi = new Pair[N];
            var cdi = new Pair[N];
            for (var i = 0; i < N; i++)
            {
                var ab = Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToArray();
                abi[i] = new Pair { X = ab[0], Y = ab[1] };
            }
            for (var i = 0; i < N; i++)
            {
                var cd = Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToArray();
                cdi[i] = new Pair { X = cd[0], Y = cd[1] };
            }
            abi = abi.OrderByDescending(x => x.Y).ToArray();
            cdi = cdi.OrderBy(x => x.X).ToArray();

            var answer = 0;
            var hash = new HashSet<int>();
            for (var i = 0; i < N; i++)
            {
                for (var j = 0; j < N; j++)
                {
                    if (!hash.Contains(j) && abi[i].X < cdi[j].X && abi[i].Y < cdi[j].Y)
                    {
                        answer++;
                        hash.Add(j);
                        break;
                    }
                }
            }

            Console.WriteLine(answer);
        }

        public class Pair
        {
            public int X { get; set; }
            public int Y { get; set; }
        }
    }
}