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;
using System.Text;
using System.Threading.Tasks;



class Program
{
    const int MOD = 1000000007;
    const int INF = 1 << 30;
    static void Main(string[] args)
    {
        Solve();
    }




    static void Solve()
    {
        Scan sc = new Scan();
        write wr = new write();

        int N = sc.intarr[0];

        var BX = new int[N];
        var BY = new int[N];
        var RX = new int[N];
        var RY = new int[N];

        int ans = 0;

        for (int i = 0; i < N; ++i)
        {
            var a = sc.intarr;
            RX[i] = a[0];
            RY[i] = a[1];
        }

        for (int i = 0; i < N; ++i)
        {
            var a = sc.intarr;
            BX[i] = a[0];
            BY[i] = a[1];
        }

        Array.Sort(BX, BY);
        for(int i = 0; i < N; ++i)
        {
            int ry = -1;
            int ryj = 0;
            for(int j = 0; j < N; ++j)
            {
                if (BX[i] > RX[j] && BY[i] > RY[j]&&RY[j]>=0)
                {
                    if (ry < RY[j])
                    {
                        ry = RY[j];
                        ryj = j;
                    }
                }
            }
            if (ry >= 0)
            {
                RY[ryj] = -1;
                ans++;
            }
        }

        wr.wri(ans);
    }
}
    




class Scan
{
        public string str => Console.ReadLine();

        public string[] strarr => str.Split(' ');

        public long[] longarr => strarr.Select(long.Parse).ToArray();
        public int[] intarr => strarr.Select(int.Parse).ToArray();
    public char[] chararr => str.ToArray();


}



class write
{
    public void wri<Type>(Type x)
    {
        Console.WriteLine(x);
    }
}