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 Ruby (2.3.3) (judge verdict: Accepted)

io = STDIN
ary=[]
$n=io.gets.to_i
$n.times do
  x,y=io.gets.split.map(&:to_i)
  ary << [x,y,:r]
end
$n.times do
  x,y=io.gets.split.map(&:to_i)
  ary << [x,y,:b]
end
ary.sort_by!{|x,y,color|x}
$ar=ary.to_enum.with_index.map{|(x,y,color),i|[x,y,color,i]}
def search_red(upper_x,upper_y)
  sel=$ar.select{|x,y,color,i|color==:r && upper_y>y && upper_x>x}
     .max_by{|x,y,color,i|y}
  if sel
    x,y,color,i = sel
    $ar[i][2] = nil
    return true
  else
    return false
  end
end
#red < blue
cnt=0
$ar.each do |x,y,color,i|
  if color == :b
    # p [$ar[i],$ar]
    if search_red(x,y)
      $ar[i][2]=nil
      cnt +=1
    end
  end
end
puts cnt