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: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace Contest
{
    class Scanner
    {
        private string[] line = new string[0];
        private int index = 0;
        public string Next()
        {
            if (line.Length <= index)
            {
                line = Console.ReadLine().Split(' ');
                index = 0;
            }
            var res = line[index];
            index++;
            return res;
        }
        public int NextInt()
        {
            return int.Parse(Next());
        }
        public long NextLong()
        {
            return long.Parse(Next());
        }
        public string[] Array()
        {
            line = Console.ReadLine().Split(' ');
            index = line.Length;
            return line;
        }
        public int[] IntArray()
        {
            var array = Array();
            var result = new int[array.Length];
            for (int i = 0; i < array.Length; i++)
            {
                result[i] = int.Parse(array[i]);
            }

            return result;
        }
        public long[] LongArray()
        {
            var array = Array();
            var result = new long[array.Length];
            for (int i = 0; i < array.Length; i++)
            {
                result[i] = long.Parse(array[i]);
            }

            return result;
        }
    }

    

    class Program
    {
        private int N;
        private int[] A, B;
        private void Scan()
        {
            var sc = new Scanner();
            N = sc.NextInt();
            A = sc.IntArray();
            B = sc.IntArray();
        }

        public void Solve()
        {
            Scan();
            var ans = 0;
            var b = 1 << 29;
            for (int i = 28; i >= 0; i--)
            {
                for (int j = 0; j < N; j++)
                {
                    A[j] %= b;
                    B[j] %= b;
                }
                Array.Sort(B);
                foreach (var j in A)
                {
                    var q1 = b / 2;
                    var q2 = q1 * 2;
                    var q3 = q1 * 3;
                    var aa = LowerBound(B, q1 - j);
                    var bb = LowerBound(B, q2 - j);
                    var cc = LowerBound(B, q3 - j);
                    ans ^= q1 * ((N - cc + bb - aa) % 2);
                }

                b /= 2;
            }
            Console.WriteLine(ans);
        }

        private int LowerBound(int[] array, int target)
        {
            int begin = -1;
            int end = N;
            while (end - begin > 1)
            {
                int mid = (begin + end) / 2;
                if (array[mid] > target)
                {
                    end = mid;
                }
                else
                {
                    begin = mid;
                }
            }

            return end;
        }

        static void Main(string[] args)
        {
            new Program().Solve();
        }
    }
}