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: Time Limit Exceeded)

using System;
using System.Linq;
using System.Collections.Generic;
using System.Numerics;
using static System.Console;

class Solver {
    Scanner sc = new Scanner();

    struct Ball {
        public int X { get; set; }
        public int Y { get; set; }
    }

    int N;

    public void Solve() {
        N = sc.nextInt();
        var red = new Ball[N];
        var blue = new Ball[N];
        for (int i = 0; i < N; i++) {
            red[i].X = sc.nextInt();
            red[i].Y = sc.nextInt();
        }
        for (int i = 0; i < N; i++) {
            blue[i].X = sc.nextInt();
            blue[i].Y = sc.nextInt();
        }

        lst = new List<Ball>[N];
        for (int i = 0; i < N; i++) {
            var tmp = new List<Ball>();
            var ball = new Ball { X = -1, Y = -1 };
            tmp.Add(ball);

            for (int j = 0; j < N; j++) {
                if (blue[i].X > red[j].X && blue[i].Y > red[j].Y) {
                    tmp.Add(red[j]);
                }
            }
            lst[i] = tmp;
        }


        for (int i = 0; i < lst[0].Count; i++) {
            var dist = new bool[2 * N];
            Sub(lst[0][i], 0, 0, dist);
        }

        WriteLine(max);
    }

    int max;
    List<Ball>[] lst;

    void Sub(Ball ball, int i, int cnt, bool[] dist) {
        if (ball.X > -1 && !dist[ball.X]) {
            dist[ball.X] = true;
            cnt++;
        }

        i++;
        if (i == N) {
            max = Math.Max(max, cnt);
            return;
        }

        for (int j = 0; j < lst[i].Count; j++) {
            
            Sub(lst[i][j], i, cnt, dist.ToArray());
        }
    }
}



class Scanner {
    string[] s;
    int i;

    char[] cs = new char[] { ' ' };

    public Scanner() {
        s = new string[0];
        i = 0;
    }

    public string next() {
        if (i < s.Length) return s[i++];
        string st = Console.ReadLine();
        while (st == "") st = Console.ReadLine();
        s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
        if (s.Length == 0) return next();
        i = 0;
        return s[i++];
    }

    public int nextInt() {


        return int.Parse(next());
    }
    public int[] ArrayInt(int N, int add = 0) {
        int[] Array = new int[N];
        for (int i = 0; i < N; i++) {
            Array[i] = nextInt() + add;
        }
        return Array;
    }

    public long nextLong() {
        return long.Parse(next());
    }

    public long[] ArrayLong(int N, long add = 0) {
        long[] Array = new long[N];
        for (int i = 0; i < N; i++) {
            Array[i] = nextLong() + add;
        }
        return Array;
    }

    public double nextDouble() {
        return double.Parse(next());
    }

    public double[] ArrayDouble(int N, double add = 0) {
        double[] Array = new double[N];
        for (int i = 0; i < N; i++) {
            Array[i] = nextDouble() + add;
        }
        return Array;
    }
}

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