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 (1.14.1) (judge verdict: Accepted)

package main

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

var sc = bufio.NewScanner(os.Stdin)

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

type point struct {
	X, Y       int
	IsSelected bool
}

type pointList []point

type redList struct{ pointList }
type blueList struct{ pointList }

func (a pointList) Len() int      { return len(a) }
func (a pointList) Swap(i, j int) { a[i], a[j] = a[j], a[i] }

func (a redList) Less(i, j int) bool  { return a.pointList[i].Y > a.pointList[j].Y }
func (a blueList) Less(i, j int) bool { return a.pointList[i].X < a.pointList[j].X }

func isClose(red, blue point) bool {
	if red.X < blue.X && red.Y < blue.Y {
		return true
	}
	return false
}

func main() {
	sc.Split(bufio.ScanWords)

	N := scanInt()
	R, B := redList{make(pointList, N)}, blueList{make(pointList, N)}
	for i := 0; i < N; i++ {
		R.pointList[i].X, R.pointList[i].Y = scanInt(), scanInt()
	}
	for i := 0; i < N; i++ {
		B.pointList[i].X, B.pointList[i].Y = scanInt(), scanInt()
	}
	sort.Sort(R)
	sort.Sort(B)

	ans := 0
	for _, blue := range B.pointList {
		for i, red := range R.pointList {
			if isClose(red, blue) && !red.IsSelected {
				ans++
				R.pointList[i].IsSelected = true
				break
			}
		}
	}

	fmt.Println(ans)
}