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"
)

type Point struct {
	x  int
	y  int
	in int
}

type Points []Point

func (l Points) Len() int {
	return len(l)
}

func (l Points) Less(i, j int) bool {
	return l[i].in < l[j].in || l[i].x*l[i].y < l[j].x*l[j].y
}

func (l Points) Swap(i, j int) {
	l[i], l[j] = l[j], l[i]
}

func main() {
	s := wordScanner()

	var n int
	scanInts(s, &n)

	reds := make(Points, n)
	for i := range reds {
		scanInts(s, &reds[i].x, &reds[i].y)
	}

	blues := make(Points, n)
	for i := range blues {
		scanInts(s, &blues[i].x, &blues[i].y)
	}

	sort.Sort(reds)

	for i, b := range blues {
		for _, r := range reds {
			if isInner(r, b) {
				blues[i].in++
			}
		}
	}
	sort.Sort(blues)

	c := 0
	for _, r := range reds {
		for j, b := range blues {
			if isInner(r, b) {
				blues = append(blues[:j], blues[j+1:]...)
				c++
				break
			}
		}
	}
	fmt.Println(c)
}

func isInner(inner, outer Point) bool {
	return outer.x > inner.x && outer.y > inner.y
}

func wordScanner() *bufio.Scanner {
	s := bufio.NewScanner(os.Stdin)
	s.Split(bufio.ScanWords)
	return s
}

func scanInts(s *bufio.Scanner, vals ...*int) {
	for i := range vals {
		s.Scan()
		n, _ := strconv.Atoi(s.Text())
		*vals[i] = n
	}
}