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;

fn read<T>() -> Vec<T>
where T:
    std::str::FromStr,
    T::Err: std::fmt::Debug {

    let mut buf = String::new();
    io::stdin().read_line(&mut buf).unwrap();
    buf.split(' ')
        .map(|s| s.trim().parse().unwrap())
        .collect()
}

fn read_one<T>() -> T
where T:
    std::str::FromStr,
    T::Err: std::fmt::Debug {

    let mut buf = String::new();
    io::stdin().read_line(&mut buf).unwrap();
    buf.trim().parse().unwrap()
}

fn main() {
    let n = read_one::<usize>();
    let mut a: Vec<(usize, usize)> = Vec::new();
    let mut b: Vec<(usize, usize)> = Vec::new();
    for _ in 0..n {
        let i = read::<usize>();
        a.push((i[0], i[1]));
    }

    for _ in 0..n {
        let i = read::<usize>();
        b.push((i[0], i[1]));
    }

    a.sort();
    a.reverse();
    b.sort();

    let mut cnt = 0;
    let mut len = a.len();
    while len > 0 && b.len() > 0 {

        let bi = b.pop().unwrap();
        let mut off = 0;
        while len > 0 && off < a.len() {
            let ai = a[off];
            if bi.0 > ai.0 && bi.1 > ai.1 { 
                cnt += 1;
                len -= 1;
                a.remove(off);
                break; 
            } else { off += 1; }
        }
    }

    println!("{}", cnt);
}