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 Go (1.6) (judge verdict: Wrong Answer)

// Package main provides
//
// File:  c.go
// Author: ymiyamoto
//
// Created on Sat Dec 29 04:55:53 2018
//
package main

import (
	"fmt"
	"sort"
)

type point struct {
	x, y int
}

func (p point) lessThan(q point) bool {
	return p.x < q.x && p.y < q.y
}

type points []point

// (p points) ...
func (p points) Less(i, j int) bool {
	if p[i].x == p[j].x {
		return p[i].y < p[j].y
	}

	return p[i].x < p[j].x
}

// (p points)Len ...
func (p points) Len() int {
	return len(p)
}

// (p points)Swap ...
func (p points) Swap(i, j int) {
	p[i], p[j] = p[j], p[i]
}
func main() {
	var N int

	fmt.Scan(&N)
	reds := make(points, N)
	for i := range reds {
		fmt.Scan(&reds[i].x, &reds[i].y)
	}
	sort.Sort(reds)

	blues := make(points, N)
	for i := range blues {
		fmt.Scan(&blues[i].x, &blues[i].y)
	}
	sort.Sort(blues)

	ans := 0
	paired := make([]bool, N)
	for _, b := range blues {
		max := -1
		pair := -1
		for j, r := range reds {
			if r.x < b.x && r.y < b.y && max < r.y && !paired[j] {
				max = r.y
				pair = j
			}
		}
		if pair != -1 {
			fmt.Println(b, reds[pair])
			paired[pair] = true
			ans++
		}
	}

	fmt.Printf("%d\n", ans)
}