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::str::FromStr;
use std::fmt::Debug;
use std::cmp;

#[allow(dead_code)]
fn read_as_vec<T>() -> Vec<T>
where T: FromStr, <T as FromStr>::Err : Debug{
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().split_whitespace().map(|c| T::from_str(c).unwrap()).collect()

}

//21:45
fn main(){
    let n: usize = read_as_vec()[0];

    let mut r: Vec<(i64, i64)> = vec![];

    for _ in 0..n{
        let line = read_as_vec::<i64>();
        r.push((line[0], line[1]));
    }

    let mut b: Vec<(i64, i64)> = vec![];

    for _ in 0..n{
        let line = read_as_vec::<i64>();
        b.push((line[0], line[1]));
    }

    let mut pairs: Vec<(usize, usize, i64)> = vec![];

    for i in 0..n{
        for j in 0..n{
            if (r[i].0 < b[j].0) && (r[i].1 < b[j].1){
                pairs.push((i,
                            j,
                            cmp::min(b[j].0-r[i].0, b[j].1-b[j].1)
                ));
            }
        }
    }

    pairs.sort_by_key(|x| x.2);
    let mut used_r: Vec<bool> = vec![false;n];
    let mut used_b: Vec<bool> = vec![false;n];

    for &pair in &pairs{
        if used_r[pair.0] == false && used_b[pair.1] == false{
            used_r[pair.0] = true;
            used_b[pair.1] = true;
        }
    }
    println!("{}", used_r.into_iter().filter(|x| *x).count());
}