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;

namespace ConsoleApp3
{
    class Program
    {

        public static int[] ReadIntArr()
        {
            return Array.ConvertAll<string, int>(Console.ReadLine().Split(' '), (x) => Convert.ToInt32(x));
        }

        public static int ReadInt()
        {
            return Convert.ToInt32(Console.ReadLine());
        }

        static void Main(string[] args)
        {
            var N = ReadInt();
            var reds = new List<int[]>();
            var blues = new List<int[]>();

            for (int i = 0; i < N; i++)
                reds.Add(ReadIntArr());
            for (int i = 0; i < N; i++)
                blues.Add(ReadIntArr());

            reds.Sort((x, y) => (x[0].CompareTo(y[0])));
            blues.Sort((x, y) => (x[0].CompareTo(y[0])));

            int cnt = 0;
            for (int i = 0; i < N; i++)
            {
                var maxY = 0;
                var maxAt = -1;
                for (int k = reds.Count - 1; k >= 0; k--)
                {
                    if (reds[k][0] < blues[i][0] && reds[k][1] < blues[i][1])
                    {
                        if (maxY <= reds[k][1])
                        {
                            maxY = reds[k][1];
                            maxAt = k;
                        }
                    }

                }

                if (maxAt >= 0)
                {
                    cnt++;
                    //Console.WriteLine("{0},{1}:{2},{3}", reds[maxAt][0], reds[maxAt][1], blues[i][0], blues[i][1]);
                    reds.RemoveAt(maxAt);
                }
            }


            Console.WriteLine(cnt);

        }
    }
}