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.Collections.Generic;
using System.Text;

namespace AtTest.C_Challenge
{
    class ABC_091
    {
        static void Main(string[] args)
        {
            Method(args);
            Console.ReadLine();
        }

        static void Method(string[] args)
        {
            int n = ReadInt();
            var ab = new int[n][];
            var cd = new int[n][];
            for (int i = 0; i < n; i++)
            {
                int[] input = ReadInts();
                ab[i] = new int[2];
                ab[i][0] = input[0];
                ab[i][1] = input[1];
            }
            for (int i = 0; i < n; i++)
            {
                int[] input = ReadInts();
                cd[i] = new int[2];
                cd[i][0] = input[0];
                cd[i][1] = input[1];
            }
            Array.Sort(ab, (a, b) => a[0] - b[0]);
            Array.Sort(cd, (a, b) => a[0] - b[0]);
            int pairCnt = 0;
            for (int i = 0; i < n; i++)
            {
                int aIndex = n - 1;
                for (; aIndex >= 0; aIndex--)
                {
                    if (ab[aIndex][0] > cd[i][0])
                    {
                        continue;
                    }
                    else
                    {
                        break;
                    }
                }
                if (aIndex == -1)
                {
                    continue;
                }
                int redIndex = -1;
                for (int j = 0; j <=aIndex; j++)
                {
                    if (cd[i][1] < ab[j][1])
                    {
                        continue;
                    }
                    else if (redIndex == -1
                            || ab[redIndex][1] < ab[j][1])
                    {
                        redIndex = j;
                    }
                }
                if (redIndex != -1)
                {
                    pairCnt++;
                    ab[redIndex][1] = 3000;
                }
            }
            Console.WriteLine(pairCnt);
        }

        private static string Read() { return Console.ReadLine(); }
        private static int ReadInt() { return int.Parse(Read()); }
        private static long ReadLong() { return long.Parse(Read()); }
        private static double ReadDouble() { return double.Parse(Read()); }
        private static int[] ReadInts() { return Array.ConvertAll(Read().Split(), int.Parse); }
        private static long[] ReadLongs() { return Array.ConvertAll(Read().Split(), long.Parse); }
        private static double[] ReadDoubles() { return Array.ConvertAll(Read().Split(), double.Parse); }
    }
}