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 Yorukatsu053.Questions;
using Yorukatsu053.Extensions;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace Yorukatsu053.Questions
{
    /// <summary>
    /// https://atcoder.jp/contests/arc092/tasks/arc092_a
    /// </summary>
    public class QuestionE : AtCoderQuestionBase
    {
        public override IEnumerable<object> Solve(TextReader inputStream)
        {
            int n = inputStream.ReadInt();
            var redPoints = new List<Point>(n);
            var bluePoints = new List<Point>(n);

            for (int i = 0; i < n; i++)
            {
                var xy = inputStream.ReadIntArray();
                redPoints.Add(new Point(xy[0], xy[1]));
            }

            for (int i = 0; i < n; i++)
            {
                var xy = inputStream.ReadIntArray();
                bluePoints.Add(new Point(xy[0], xy[1]));
            }

            redPoints.Sort((p1, p2) => p2.Y - p1.Y);
            bluePoints.Sort((p1, p2) => p1.X - p2.X);

            var pairCount = 0;
            foreach (var bluePoint in bluePoints)
            {
                if (redPoints.Any(p => p.X < bluePoint.X))
                {
                    var removed = redPoints.First(p => p.X < bluePoint.X);
                    redPoints.Remove(removed);
                    pairCount++;
                }
            }

            yield return pairCount;
        }

        struct Point : IEquatable<Point>
        {
            public int X { get; }
            public int Y { get; }

            public Point(int x, int y)
            {
                X = x;
                Y = y;
            }

            public override bool Equals(object obj)
            {
                return obj is Point && Equals((Point)obj);
            }

            public bool Equals(Point other)
            {
                return X == other.X &&
                       Y == other.Y;
            }

            public override int GetHashCode()
            {
                unchecked
                {
                    int hashCode = 1861411795;
                    hashCode = hashCode * -1521134295 + X.GetHashCode();
                    hashCode = hashCode * -1521134295 + Y.GetHashCode();
                    return hashCode;
                }
            }

            public static bool operator ==(Point left, Point right)
            {
                return left.Equals(right);
            }

            public static bool operator !=(Point left, Point right)
            {
                return !(left == right);
            }
        }
    }
}

namespace Yorukatsu053
{
    class Program
    {
        static void Main(string[] args)
        {
            IAtCoderQuestion question = new QuestionE();    // 問題に合わせて書き換え
            var answers = question.Solve(Console.In);
            foreach (var answer in answers)
            {
                Console.WriteLine(answer);
            }
        }
    }
}

#region Base Classes

namespace Yorukatsu053.Questions
{

    public interface IAtCoderQuestion
    {
        IEnumerable<object> Solve(string input);
        IEnumerable<object> Solve(TextReader inputStream);
    }

    public abstract class AtCoderQuestionBase : IAtCoderQuestion
    {
        public IEnumerable<object> Solve(string input)
        {
            var stream = new MemoryStream(Encoding.Unicode.GetBytes(input));
            var reader = new StreamReader(stream, Encoding.Unicode);

            return Solve(reader);
        }

        public abstract IEnumerable<object> Solve(TextReader inputStream);
    }

}

#endregion

#region Extensions

namespace Yorukatsu053.Extensions
{
    internal static class TextReaderExtensions
    {
        internal static int ReadInt(this TextReader reader) => int.Parse(ReadString(reader));
        internal static long ReadLong(this TextReader reader) => long.Parse(ReadString(reader));
        internal static double ReadDouble(this TextReader reader) => double.Parse(ReadString(reader));
        internal static string ReadString(this TextReader reader) => reader.ReadLine();

        internal static int[] ReadIntArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(int.Parse).ToArray();
        internal static long[] ReadLongArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(long.Parse).ToArray();
        internal static double[] ReadDoubleArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(double.Parse).ToArray();
        internal static string[] ReadStringArray(this TextReader reader, char separator = ' ') => reader.ReadLine().Split(separator);
    }
}

#endregion