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: Wrong Answer)

use std::io::{BufRead, Write};
use std::io;

fn solve<R: BufRead, W: Write>(mut input: R, mut output: W) {
    let mut buf = String::new();
    input.read_line(&mut buf).unwrap();
    let n: usize = buf.trim_right().parse().unwrap();
    let mut a: Vec<(usize, usize)> = (0..n).map(|_| {
        buf.clear();
        input.read_line(&mut buf).unwrap();
        let mut split = buf.split_whitespace();
        (split.next().unwrap().parse().unwrap(), split.next().unwrap().parse().unwrap())
    }).collect();
    let mut b: Vec<(usize, usize)> = (0..n).map(|_| {
        buf.clear();
        input.read_line(&mut buf).unwrap();
        let mut split = buf.split_whitespace();
        (split.next().unwrap().parse().unwrap(), split.next().unwrap().parse().unwrap())
    }).collect();
    loop {
        if let Some((viable, _)) = a.iter().cloned().map(|(x1, y1)| {
            b.iter().cloned().filter(|&(x2, y2)| x2 > x1 && y2 > y1).count()
        }).enumerate().filter(|&(_, i)| i != 0).min_by_key(|&(_, i)| i) {
            let (x1, y1) = a.remove(viable);
            let first_b = b.iter().cloned().position(|(x2, y2)| x2 > x1 && y2 > y1).unwrap();
            b.remove(first_b);
        } else {
            break;
        }
    }
    writeln!(output, "{}", n - a.len()).unwrap();
}

fn main() {
    let stdin = io::stdin();
    let stdout = io::stdout();
    solve(stdin.lock(), stdout.lock());
}

#[cfg(test)]
mod tests {
    fn test(input: &str, output: &str) {
        let mut v: Vec<u8> = Vec::new();
        ::solve(input.as_bytes(), &mut v);
        assert_eq!(String::from_utf8(v).unwrap(), output);
    }

    #[test]
    fn case1() {
        test(
            "3
2 0
3 1
1 3
4 2
0 4
5 5
",
            "2\n",
        );
    }

    #[test]
    fn case2() {
        test(
            "3
0 0
1 1
5 2
2 3
3 4
4 5
",
            "2\n",
        );
    }

    #[test]
    fn case3() {
        test(
            "2
2 2
3 3
0 0
1 1
",
            "0\n",
        );
    }

    #[test]
    fn case4() {
        test(
            "5
0 0
7 3
2 2
4 8
1 6
8 5
6 9
5 4
9 1
3 7
",
            "5\n",
        );
    }
}