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: Time Limit Exceeded)

N = gets.to_i
a = N.times.map{gets.split.map &:to_i}
b = N.times.map{gets.split.map &:to_i}
a.sort_by!{|x,y|[-x, -y]}
b.sort_by!{|x,y|[x, y]}

usedb = [false]*N

ans = 0
dfs = ->ai, n{
  return if ai >= a.size
  ax, ay = a[ai]
  fbx = fby = nil
  b.each_with_index{|(bx, by), bi|
    # p [[ax,ay], [bx,by]]
    next if usedb[bi]
    next if !(bx > ax && by > ay)
    fbx ||= bx
    fby ||= by
    break if bx > fbx && by > fby
    usedb[bi] = true
    ans = n+1 if n+1 > ans
    dfs[ai+1, n+1]
    usedb[bi] = false
  }
  dfs[ai+1, n]
}

dfs[0, 0]
p ans