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 Rust (1.42.0) (judge verdict: Accepted)

use std::io::Read;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();

    let answer = solve(&buf);

    println!("{}", answer);
}

fn solve(input: &str) -> String {
    let mut iterator = input.split_whitespace();

    let n: usize = iterator.next().unwrap().parse().unwrap();
    let mut reds: Vec<(usize, usize)> =
        (0..n)
            .map(|_| {
                let ai: usize = iterator.next().unwrap().parse().unwrap();
                let bi: usize = iterator.next().unwrap().parse().unwrap();
                (ai, bi)
            })
            .collect();
    let mut blues: Vec<(usize, usize)> =
        (0..n)
            .map(|_| {
                let ci: usize = iterator.next().unwrap().parse().unwrap();
                let di: usize = iterator.next().unwrap().parse().unwrap();
                (ci, di)
            })
            .collect();

    reds.sort_by_key(|it| 1000 - it.1);
    blues.sort();

    let mut ans: usize = 0;
    let mut used: Vec<bool> = vec![false; n];
    for i in 0..n {
        for j in 0..n {
            if used[j] {
                continue;
            }
            if reds[j].0 < blues[i].0 && reds[j].1 < blues[i].1 {
                ans += 1;
                used[j] = true;
                break;
            }
        }
    }
    ans.to_string()
}