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

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

func out(x ...interface{}) {
	fmt.Println(x...)
}

var sc = bufio.NewScanner(os.Stdin)

func getInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func getString() string {
	sc.Scan()
	return sc.Text()
}

// min, max, asub, absなど基本関数
func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func asub(a, b int) int {
	if a > b {
		return a - b
	}
	return b - a
}

func abs(a int) int {
	if a >= 0 {
		return a
	}
	return -a
}

type point struct {
	x, y int
	n    int
}

// Data :
type Data struct {
	X, n int
}

// Datas :
type Datas []Data

func (p Datas) Len() int {
	return len(p)
}

func (p Datas) Swap(i, j int) {
	p[i], p[j] = p[j], p[i]
}

func (p Datas) Less(i, j int) bool {
	return p[i].X < p[j].X
}

func main() {
	sc.Split(bufio.ScanWords)
	N := getInt()
	ab := make([]point, N)
	cd := make([]point, N)
	for i := 0; i < N; i++ {
		ab[i].x, ab[i].y = getInt(), getInt()
	}
	for i := 0; i < N; i++ {
		cd[i].x, cd[i].y = getInt(), getInt()
	}

	vec := make([][]point, N)
	num := make(Datas, N)
	for i := 0; i < N; i++ {
		for j := 0; j < N; j++ {
			dx := cd[j].x - ab[i].x
			dy := cd[j].y - ab[i].y
			if dx > 0 && dy > 0 {
				vec[i] = append(vec[i], point{dx, dy, j})
			}
		}
		num[i] = Data{len(vec[i]), i}
	}
	sort.Sort(num)
	// out(vec)
	// out(num)
	ans := 0
	used := make([]bool, N)
	for i := 0; i < N; i++ {
		for _, v := range vec[num[i].n] {
			if used[v.n] != true {
				used[v.n] = true
				ans++
				break
			}
		}
	}
	out(ans)
}