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.Linq;
using System.Collections.Generic;

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            ARC092.C();
        }
        class ARC092
        {
            public static void C()
            {
                var N = Read.Int();
                var AB = Read.TupleInt(N).OrderBy(x => -x.Item1).ToArray();
                var CD = Read.TupleInt(N).OrderBy(x => -x.Item1).ToArray();
                var matched = new bool[N];
                for(int i = 0; i < N; ++i)
                {
                    var A = AB[i].Item1;
                    var B = AB[i].Item2;
                    int idx = -1;
                    int min = 1000;
                    for(int j = 0; j < N; ++j)
                    {
                        if (!matched[j])
                        {
                            var C = CD[j].Item1;
                            var D = CD[j].Item2;
                            if (A < C && B < D && D < min)
                            {
                                idx = j;
                                min = D;
                            }
                        }
                    }
                    if (idx >= 0) { matched[idx] = true; }
                }
                Console.WriteLine(matched.Count(x => x));
            }
            public static void D()
            {
                var N = Read.Int();
                var A = Read.IntN();
                var B = Read.IntN();

                Func<int[], int, Tuple<int[], int[]>> gen01 = (X, i) =>
                {
                    var L0 = new List<int>();
                    var L1 = new List<int>();
                    foreach(var x in X)
                    {
                        var v = x % (1 << i + 1);
                        (((v & (1 << i)) > 0) ? L1 : L0).Add(v % (1 << i));
                    }
                    var A0 = L0.ToArray();
                    var A1 = L1.ToArray();
                    Array.Sort(A0);
                    Array.Sort(A1);
                    return new Tuple<int[], int[]>(A0, A1);
                };
                Func<int[], int[], int, bool,  long> count1 = (X, Y, keta, isSame) =>
                {
                    var K = 1 << keta;
                    long count = 0;
                    int right = Y.Length;
                    for(int i = 0; i < X.Length; ++i)
                    {
                        while (right > 0 && X[i] + Y[right - 1] >= K) { right--; }
                        count += (Y.Length - right);
                    }
                    return isSame ? count : (long)X.Length * Y.Length - count;
                };

                int ans = 0;
                for (int i = 0; i < 30; ++i)
                {
                    var AT = gen01(A, i);
                    var BT = gen01(B, i);
                    var count = count1(AT.Item1, BT.Item1, i, true) + count1(AT.Item1, BT.Item2, i, false)
                        + count1(AT.Item2, BT.Item1, i, false) + count1(AT.Item2, BT.Item2, i, true);
                    if (count % 2 > 0) { ans += 1 << i; }
                }
                Console.WriteLine(ans);
            }
        }



        class Util
        {
        }

        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M, bool isDirectional = false)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i) { dict.Add(i, new HashSet<int>()); }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN(); dict[ab[0]].Add(ab[1]);
                    if (!isDirectional) { dict[ab[1]].Add(ab[0]); }
                }
                return dict;
            }
            public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
            {
                Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new Dictionary<int, long>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1], ab[2]);
                    dict[ab[1]].Add(ab[0], ab[2]);
                }
                return dict;
            }
        }
    }
}