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 (2.7.1) (judge verdict: Runtime Error)

N=gets.to_i
red=[]
N.times{
	a,b=gets.split.map(&:to_i)
	red << [a,b]
}
blue=[]
N.times{
	c,d=gets.split.map(&:to_i)
	blue << [c,d]
}
red.sort!
blue.sort!
warn red.inspect
warn blue.inspect
r=0
until red.empty? || blue.empty?
	if blue[0][0] <= red[0][0]
		blue.shift
		next
	end
	i=-1
	max_i=nil
	while i<red.size-1
		i+=1
		break if red[i][0]>=blue[0][0]
		next if red[i][1]>blue[0][1]
		if !max_i || red[i][1] > red[max_i][1]
			max_i = i
		end
	end
	warn [max_i, red[max_i], blue[0]].inspect
	r+=1
	red.delete_at(max_i)
	blue.shift
end
puts r