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)

#[test]
fn test_solve() {
    assert_eq!(solve("3\n2 0\n3 1\n1 3\n4 2\n0 4\n5 5\n"), "2\n");
    assert_eq!(solve("3\n0 0\n1 1\n5 2\n2 3\n3 4\n4 5\n"), "2\n");
    assert_eq!(solve("2\n2 2\n3 3\n0 0\n1 1\n"), "0\n");
    assert_eq!(
        solve("5\n0 0\n7 3\n2 2\n4 8\n1 6\n8 5\n6 9\n5 4\n9 1\n3 7\n"),
        "5\n"
    );
    assert_eq!(
        solve("5\n0 0\n1 1\n5 5\n6 6\n7 7\n2 2\n3 3\n4 4\n8 8\n9 9\n"),
        "4\n"
    );
}
fn solve(src: &str) -> String {
    let mut sc = Scanner::from_str(src);

    let n: usize = sc.read();
    let mut ab: Vec<(usize, usize)> = (0..n).map(|_| (sc.read(), sc.read())).collect();
    let mut cd: Vec<(usize, usize)> = (0..n).map(|_| (sc.read(), sc.read())).collect();
    ab.sort();
    cd.sort();

    let mut ans = 0;
    let mut prd = vec![false; n];
    for i in 0..n {
        let mut p = None;
        for j in 0..n {
            if ab[j].0 >= cd[i].0 {
                break;
            }
            if !prd[j] && ab[j].1 < cd[i].1 {
                p = Some(p.map_or((j, ab[j].1), |(jy, y)| {
                    if y > ab[j].1 {
                        (jy, y)
                    } else {
                        (j, ab[j].1)
                    }
                }));
            }
        }
        if let Some((j, _)) = p {
            ans += 1;
            prd[j] = true;
        }
    }

    format!("{}\n", ans)
}
fn main() {
    let mut buf = String::new();
    use std::io::{Read, Write};
    std::io::stdin().read_to_string(&mut buf).unwrap();
    std::io::stdout().write_all(solve(&buf).as_bytes()).unwrap();
}
struct Scanner<'a>(std::str::SplitWhitespace<'a>);
impl<'a> Scanner<'a> {
    fn from_str(src: &str) -> Scanner {
        Scanner(src.split_whitespace())
    }
    fn get(&mut self) -> &str {
        self.0.next().unwrap()
    }
    fn read<T: std::str::FromStr>(&mut self) -> T {
        self.get().parse().ok().unwrap()
    }
}