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: Accepted)

package main
import (
  "fmt"
  "sort"
)
func main() {
  var n,x,y,m int
  red := Points{}
  blue := Points{}
  fmt.Scan(&n)
  for i:=0;i<n;i++ {
    fmt.Scan(&x,&y)
    red = append(red,Point{x,y})
  }
  for i:=0;i<n;i++ {
    fmt.Scan(&x,&y)
    blue = append(blue,Point{x,y})
  }
  sort.Sort(sort.Reverse(red))
  sort.Sort(blue)
  m = 0
  for j:=0;j<blue.Len();j++ {
    p := Point{blue[j].x-1,-1}
    k := -1
    for i:=0;i<red.Len();i++ {
      if red[i].x < blue[j].x && red[i].y < blue[j].y &&
      p.y < red[i].y {
        p = red[i]
        k = i
      }
    }
    if k >= 0 {
      red[k] = Point{100000,100000}
      m++
    }
  }
  fmt.Println(m)
}
func abs(n int) int {
  if n < 0 { return -n }
  return n
}
type Point struct {
  x int
  y int
}
func(p Point) equals(t Point) bool {
  return p.x == t.x && p.y == t.y
}
type Points []Point
func(ps Points) Len() int {
  return len(ps)
}
func(ps Points) Swap(i,j int) {
  ps[i],ps[j] = ps[j],ps[i]
}
func(ps Points) Less(i,j int) bool {
  if ps[i].x == ps[j].x {
    return ps[i].y < ps[j].y
  } else {
    return ps[i].x < ps[j].x
  }
}