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# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Linq;
using System.Collections.Generic;
using static System.Console;
using System.Text;
using System.IO;
using static System.Math;
using System.Numerics;

namespace AtCoder
{
    class Program
    {
        static public long[] Sarray() { return ReadLine().Split().Select(long.Parse).ToArray(); }
        static public List<long> Slist() { return ReadLine().Split().Select(long.Parse).ToList(); }
        static long Mod = (long)1e9 + 7;
        static void Main(string[] args)
        {
            SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
            Solve();
            Out.Flush();
            Read();
        }
        static void Solve()
        {
            var N = Sarray()[0];

            var rPts = new Tuple<long, long>[N];
            var bPts = new Tuple<long, long>[N];
            for (var i = 0; i < N; ++i)
            {
                var ab = Sarray();
                rPts[i] = Tuple.Create(ab[0], ab[1]);
            }
            for (var i = 0; i < N; ++i)
            {
                var cd = Sarray();
                bPts[i] = Tuple.Create(cd[0], cd[1]);
            }
            var rPairs = new List<HashSet<Tuple<long, long>>>();
            var bCount = new Dictionary<Tuple<long, long>, long>();
            for (var i = 0; i < N; ++i)
            {
                rPairs.Add(bPts.Where(b => rPts[i].Item1 < b.Item1 && rPts[i].Item2 < b.Item2).ToHashSet());
                bCount[bPts[i]] = rPts.Where(r => r.Item1 < bPts[i].Item1 && r.Item2 < bPts[i].Item2).Count();
            }
            rPairs.Sort((l, r) => r.Count.CompareTo(l.Count));
            var ans = 0L;
            while (rPairs.Any())
            {
                var lst = rPairs.Count - 1;
                if (0 == rPairs[lst].Count)
                {
                    rPairs.RemoveAt(lst);
                    continue;
                }
                var min = N + 1;
                var sel = new Tuple<long, long>(0, 0);
                foreach (var rpt in rPairs[lst])
                {
                    if (bCount[rpt] < min)
                    {
                        min = bCount[rpt];
                        sel = rpt;
                    }
                }
                ++ans;
                rPairs.RemoveAt(lst);
                foreach (var rpt in rPairs)
                    rpt.Remove(sel);
            }
            WriteLine(ans);
        }
    }
}