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"
)

var sc = bufio.NewScanner(os.Stdin)

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

type Sort1 [][]int

func (x Sort1) Len() int           { return len(x) }
func (x Sort1) Less(i, j int) bool { return x[i][1] > x[j][1] }
func (x Sort1) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }

type Sort0 [][]int

func (x Sort0) Len() int           { return len(x) }
func (x Sort0) Less(i, j int) bool { return x[i][0] > x[j][0] }
func (x Sort0) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }

func main() {
	buf := make([]byte, 0)
	sc.Buffer(buf, 1000000009)
	sc.Split(bufio.ScanWords)
	n, _ := strconv.Atoi(Scanner())
	ab := make([][]int, n)
	cd := make([][]int, n)
	for i := 0; i < n; i++ {
		a, _ := strconv.Atoi(Scanner())
		b, _ := strconv.Atoi(Scanner())
		ab[i] = []int{a, b}
	}
	for i := 0; i < n; i++ {
		c, _ := strconv.Atoi(Scanner())
		d, _ := strconv.Atoi(Scanner())
		cd[i] = []int{c, d}
	}
	sort.Stable(Sort1(ab))
	sort.Stable(Sort0(ab))
	sort.Stable(Sort1(cd))
	sort.Stable(Sort0(cd))
	ans := 0
	list := make([]bool, n)
	for i := 0; i < n; i++ {
		c, d := cd[i][0], cd[i][1]
		for j := 0; j < n; j++ {
			a, b := ab[j][0], ab[j][1]
			if !list[j] && a < c && b < d {
				list[j] = true
				ans += 1
				break
			}
		}
	}
	fmt.Println(ans)
}