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.Generic;
using System.Linq;

namespace AtCoder
{
    class Program
    {
        static List<Coordinate> red;
        static List<Coordinate> blue;

        static void Main(string[] args)
        {
            //[summary]C - 2D Plane 2N Points
            int N = int.Parse(Console.ReadLine());

            red = GetCoordinates(N);
            blue = GetCoordinates(N);

            //赤い点は y座標の降順にソート
            red = red.OrderByDescending(c => c.y).ToList();

            //青い点は y座標の昇順にソート
            blue = blue.OrderBy(c => c.y).ToList();

            foreach (var b in blue)
            {
                GetPair(b.y, b.x);
            }

            Console.WriteLine(N - red.Count);
        }

        static void GetPair(int y, int x)
        {
            for (int i = 0; i < red.Count; i++)
            {
                //赤い点のy座標が初めて青い点のy座標より小さくなったとき
                //それ以降の赤い点に対して、x座標が最大の点を求める
                if (red[i].y < y)
                {
                    GetMaxX(i, x);
                    return;
                }
            }
        }

        static void GetMaxX(int start, int x)
        {
            int max = -1;
            int index = 0;

            for(int i = start; i < red.Count; i++)
            {
                if (red[i].x < x && red[i].x > max)
                {
                    max = red[i].x;
                    index = i;
                }
            }

            if (max > -1)
            {
                red.RemoveAt(index);
            }
        }

        static List<Coordinate> GetCoordinates(int N)
        {
            var coords = new List<Coordinate>();

            for (int i = 0; i < N; i++)
            {
                var line = ReadLine();
                int y = line[0];
                int x = line[1];

                coords.Add(new Coordinate(y, x));
            }

            return coords;
        }

        static List<int> ReadLine()
        {
            var line = Console.ReadLine();
            var arr = line.Split(' ');

            return arr.Select(x => int.Parse(x)).ToList();
        }

        struct Coordinate
        {
            public int y;
            public int x;

            public Coordinate(int y, int x)
            {
                this.y = y;
                this.x = x;
            }
        }
    }
}