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)

use std::io::*;
use std::str::*;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let s = stdin
        .bytes()
        .map(|c| c.unwrap() as char)
        .take_while(|c| !c.is_whitespace())
        .collect::<String>();
    s.parse::<T>().ok().unwrap()
}

#[derive(Debug)]
struct Point {
    x: u32,
    y: u32,
    pair: bool,
}

fn main() {
    let n: usize = read();
    let mut red_points: Vec<Point> = Vec::new();
    let mut pair = 0;
    for _ in 0..n {
        let x = read();
        let y = read();
        red_points.push(Point {
            x: x,
            y: y,
            pair: false,
        });
    }
    red_points.sort_by(|m, n| n.y.cmp(&m.y));
    let mut blue_points: Vec<Point> = Vec::new();
    for _ in 0..n {
        let x = read();
        let y = read();
        blue_points.push(Point {
            x: x,
            y: y,
            pair: false,
        });
    }
    blue_points.sort_by(|m, n| m.x.cmp(&n.x));
    for bp in blue_points.iter_mut() {
        for rp in red_points.iter_mut() {
            if rp.x < bp.x && rp.y < bp.y {
                if !(rp.pair || bp.pair) {
                    rp.pair = true;
                    bp.pair = true;
                    pair += 1;
                }
            }
        }
    }
    println!("{}", pair);
}