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;
using static System.Console;

namespace For_Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(ReadLine());
            var points = new List<NPoint>();
            for(int i = 0; i < 2 * n; i++)
            {
                string[] inf = ReadLine().Split(' ');
                points.Add(new NPoint(int.Parse(inf[0]), int.Parse(inf[1]), i / n));
            }
            int ans = 0;

            NPoint[] points2 = points.OrderByDescending(x => x.y).OrderByDescending(x => x.x).ToArray();
            int count = 0;
            again:;
            NPoint blueone = new NPoint(0, 0, -1);
            for(int i = 0; i < n * 2; i++)
            {
                if(blueone.color == -1)//not find yet
                {
                    if (points2[i].color == 1)
                    {
                        blueone = points2[i];
                        points2[i].color = -1;
                        count++;
                    }
                }
                else
                {
                    if (points2[i].color == 0)
                    {
                        if (points2[i].y < blueone.y)
                        {
                            ans += 1;
                            points2[i].color = -1;
                            goto again;
                        }
                    }
                }
            }
            if (count < n)
            {
                goto again;
            }
            
            WriteLine(ans);
        }
    }

    struct NPoint
    {
        public int x;
        public int y;
        public int color;//0=red 1=blue
        public NPoint(int a,int b,int col)
        {
            x = a;
            y = b;
            color = col;
        }
    }
}