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 (1.15.1) (judge verdict: Accepted)

#[derive(Clone, Debug)]
struct Point {
    x: i32,
    y: i32,
    t: String
}

fn main() {
    let n = read();
    let mut vec = Vec::new();

    for _ in 0..n {
        let v = read_line();
        vec.push( Point{x: v[0], y: v[1], t: "red".to_string()} )
    }
    for _ in 0..n {
        let v = read_line();
        vec.push( Point{x: v[0], y: v[1], t: "blue".to_string()} )
    }

    // Rule
    // red.x < blue.x
    // and
    // red.y < blue.y
    vec.sort_by(|a, b| a.x.cmp(&b.x));

    let mut cnt = 0;
    loop {
        for i in 0..vec.len() as usize {
            // let mut red;
            if vec[i].t == "blue" {
                let mut max_red_y = -1;
                let mut max_red_idx : usize = std::usize::MAX;
                for j in 0..i {
                    if vec[j].t == "red" {
                        if vec[i].x > vec[j].x && vec[i].y > vec[j].y {
                            if max_red_y < vec[j].y {
                                max_red_y = vec[j].y;
                                max_red_idx = j;
                            }
                        }
                    }
                }
                if max_red_idx == std::usize::MAX {
                    // 条件を満たす赤点はなかった。青だけ消す
                    vec.remove(i);
                    break;
                } else {
                    vec.remove(max_red_idx);
                    vec.remove(i - 1);
                    cnt += 1;
                    break;
                }
            }
        }
        let mut exist_blue = false;
        for i in 0..vec.len() {
            if vec[i].t == "blue" {
                exist_blue = true;
                break;
            }
        }
        if !exist_blue {
            break;
        }
    }

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

fn read() -> i32 {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_line() -> Vec<i32> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let v = s.trim()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect();
    return v
}