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)

fn main() {
    let n = read::<usize>();
    let mut red: Vec<(usize, usize)> = Vec::new();
    let mut blue: Vec<(usize, usize)> = Vec::new();
    for _ in 0..n {
        let (x, y) = read_tuple();
        red.push((x, y));
    }
    for _ in 0..n {
        let (x, y) = read_tuple();
        blue.push((x, y));
    }

    println!("{}", solve(red, blue));
}

const INF: usize = 1000;

fn solve(mut red: Vec<(usize, usize)>, mut blue: Vec<(usize, usize)>) -> usize {
    red.sort_by(|a, b| b.0.cmp(&a.0)); // desc
    blue.sort_by(|a, b| a.0.cmp(&b.0)); // asc

    let mut cnt = 0;
    for i in 0..red.len() {
        let (a, b) = (red[i].0, red[i].1);

        let mut ymin = INF;
        let mut index = INF;
        for j in 0..blue.len() {
            let (c, d) = (blue[j].0, blue[j].1);
            if a < c && b < d {
                if d < ymin {
                    ymin = d;
                    index = j;
                }
            }
        }

        if index != INF {
            cnt += 1;
            blue[index] = (INF, INF);
        }
    }
    cnt
}

#[test]
fn test1() {
    let red = vec![(2, 0), (3, 1), (1, 3)];
    let blue = vec![(4, 2), (0, 4), (5, 5)];
    assert_eq!(2, solve(red, blue));
}

#[test]
fn test2() {
    let red = vec![(0, 0), (1, 1), (5, 2)];
    let blue = vec![(2, 3), (3, 4), (4, 5)];
    assert_eq!(2, solve(red, blue));
}

#[test]
fn test3() {
    let red = vec![(2, 2), (3, 3)];
    let blue = vec![(0, 0), (1, 1)];
    assert_eq!(0, solve(red, blue));
}

#[test]
fn test4() {
    let red = vec![(0, 0), (7, 3), (2, 2), (4, 8), (1, 6)];
    let blue = vec![(8, 5), (6, 9), (5, 4), (9, 1), (3, 7)];
    assert_eq!(5, solve(red, blue));
}

#[test]
fn test5() {
    let red = vec![(0, 0), (1, 1), (5, 5), (6, 6), (7, 7)];
    let blue = vec![(2, 2), (3, 3), (4, 4), (8, 8), (9, 9)];
    assert_eq!(4, solve(red, blue));
}

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

fn read_tuple() -> (usize, usize) {
    let v = read_vec::<usize>();
    (v[0], v[1])
}

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