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: Wrong Answer)

n = gets.to_i

x1 = Array.new
y1 = Array.new
[*0..(n-1)].each{|i|
  x1[i], y1[i] = gets.chomp.split(' ').map(&:to_i)
}

x2 = Array.new
y2 = Array.new
[*0..(n-1)].each{|i|
  x2[i], y2[i] = gets.chomp.split(' ').map(&:to_i)
}

#ary = Array.new( n, Array.new(n, nil) )
ary = Array.new( n, nil )
[*0..(n-1)].each{|i|
  ary[i] = Array.new(n, nil)
}
#p ary

[*0..(n-1)].each{|i|
  [*0..(n-1)].each{|j|
    if (x1[i] < x2[j]) and (y1[i] < y2[j]) then
      ary[i][j] = 1
    else
      ary[i][j] = 0
    end
  }
}
#p ary

ary2 = Array.new
[*0..(n-1)].each{|i|
  sum = 0
  [*0..(n-1)].each{|j|
    sum += 1 if ary[i][j] == 1
  }
  ary2[i] = sum
}

ary2 = ary2.sort
#p ary2

[*0..(n-1)].each{|i|
  ary2[i] -= (i + 1)
}

#p ary2
#p ary2.min
puts n + ary2.min