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 C
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = Input.GetN();
            var redCoordinates = Input.ReadLinesToPairList(N).OrderBy(p => p).ToList();
            var blueCoordinates = Input.ReadLinesToPairList(N).OrderBy(p => p).ToList();
            int sum = 0;
            for(int i = 0; i < redCoordinates.Count; i++)
            {
                var rpair = redCoordinates[i];
                for(int j = 0; j < blueCoordinates.Count; j++)
                {
                    var bpair = blueCoordinates[j];
                    if(rpair.CompareTo(bpair) < 0)
                    {
                        sum++;
                        blueCoordinates.Remove(bpair);
                        break;
                    }

                }
            }
            Console.WriteLine(sum);
        }
    }

    public static class Input
    {
        public static int GetN()
        {
            return int.Parse(Console.ReadLine());
        }

        public static List<List<int>> ReadLinesToIntListList(int n)
        {
            List<List<int>> list = new List<List<int>>();
            for (int i = 0; i < n; i++)
            {
                var temp = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToList();
                list.Add(temp);
            }
            return list;
        }

        public static List<Pair<int, int>> ReadLinesToPairList(int n)
        {
            List<Pair<int, int>> list = new List<Pair<int, int>>();
            for (int i = 0; i < n; i++)
            {
                var temp = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToList();
                int a = temp[0];
                int b = temp[0];
                var pair = new Pair<int, int>(a, b);
                list.Add(pair);
            }
            return list;
        }

        public static List<int> ReadLinesToIntList(int n)
        {
            List<int> list = new List<int>();
            for (int i = 0; i < n; i++)
            {
                var temp = int.Parse(Console.ReadLine());
                list.Add(temp);
            }
            return list;
        }

    }

    public class Pair<T, U> : IComparable<Pair<T, U>> where T : IComparable<T> where U : IComparable<U>
    {
        public T v1;
        public U v2;
        public Pair(T v1, U v2)
        {
            this.v1 = v1;
            this.v2 = v2;
        }
        public int CompareTo(Pair<T, U> a) => v1.CompareTo(a.v1) != 0 ? v1.CompareTo(a.v1) : v2.CompareTo(a.v2);
        public override string ToString() => v1 + " " + v2;
    }
}