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 System.Threading.Tasks;

namespace ABC091C
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());

            List<Point> R = new List<Point>();
            List<Point> B = new List<Point>();
            for (int i = 0; i < N; i++)
            {
                var line = Console.ReadLine().Split().Select(int.Parse).ToArray();
                R.Add(new Point(line[0], line[1], 0));
            }
            for (int i = 0; i < N; i++)
            {
                var line = Console.ReadLine().Split().Select(int.Parse).ToArray();
                B.Add(new Point(line[0], line[1], 1));
            }

            R.OrderBy(x => x.d).ToList();
            int ans = Solve(R, B);
            

            Console.WriteLine(ans);
            Console.ReadKey();
        }

        static int Solve(List<Point> R, List<Point> B)
        {
            int max = 0;
            if (R.Count == 0) return 0;
            List<Point> nextB = B.Where(X => X.x > R[0].x && X.y > R[0].y).ToList();
            if (nextB.Count == 0) return 0;
            R.RemoveAt(0);
            for (int i = 0; i < nextB.Count; i++)
            {
                Point temp = nextB[i];
                int tmp = B.IndexOf(nextB[i]);
                B.RemoveAt(tmp);
                max = Math.Max(max, Solve(R, B) + 1);
                B.Insert(tmp, temp);
            }
            return max;
        }
    }

    class Point
    {
        public int x;
        public int y;
        public int d;
        public Point(int a,int b, int rb)//rb 0r 1b
        {
            x = a;y = b;
            this.d = a + b;
        }
    }
}