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 next() string {
	sc.Scan()
	return sc.Text()
}

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

type Point struct {
	X int
	Y int
}

type Points []Point

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

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

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

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

	N := nextInt()
	var reds, blues []Point
	for i := 0; i < N; i++ {
		reds = append(reds, Point{nextInt(), nextInt()})
	}
	for i := 0; i < N; i++ {
		blues = append(blues, Point{nextInt(), nextInt()})
	}

	sort.Sort(Points(blues))

	c := 0
	for _, b := range blues {
		redPos := -1
		for pos, r := range reds {
			maxYRed := Point{-1, -1}
			if b.X > r.X && b.Y > r.Y {
				if maxYRed.Y < r.Y {
					maxYRed = r
					redPos = pos
				}
			}
		}

		if redPos != -1 {
			reds = append(reds[:redPos], reds[redPos+1:]...)
			c++
		}
	}

	fmt.Println(c)
}