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.chomp.to_i
a_list = []
b_list = []
c_list = []
d_list = []
for i in 0..(n-1) do
  a, b = gets.chomp.split(" ").map(&:to_i)
  a_list.push(a);
  b_list.push(b);
end
for i in 0..(n-1) do
  c, d = gets.chomp.split(" ").map(&:to_i)
  c_list.push(c);
  d_list.push(d);
end

#p a_list
#p b

Po = Struct.new(:x, :y, :reg)
r_list = []
for i in 0..(n-1) do
  r_list.push(Po.new(a_list[i], b_list[i], false))
end
b_list = []
for i in 0..(n-1) do
  b_list.push(Po.new(c_list[i], d_list[i], false))
end

r_list.sort! {|a, b| b.x * 10000 + b.y <=> a.x * 10000 + a.y}
b_list.sort! {|a, b| a.x * 10000 + a.y <=> b.x * 10000 + b.y}
#b_list.sort! {|a, b| a.x + a.y <=> b.x + b.y}

#p r_list
#p b_list

pair = 0
for i in 0..(n-1) do
    a = r_list[i].x
    b = r_list[i].y

    for j in 0..(n-1) do
        c = b_list[j].x
        d = b_list[j].y

        if a < c && b < d && !b_list[j].reg then
            b_list[j].reg = true
            pair += 1
            break
        end
    end
end

print pair