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)

fn main() {
    let n = read::<u32>();
    let mut red: Vec<((u32, u32), u32)> = Vec::new();
    let mut blue: Vec<((u32, u32), u32)> = Vec::new();
    for _ in 0..n {
        let (x, y) = read_tuple();
        let mut z = 0;
        if x > y {
            z = y.clone();
        } else {
            z = x.clone();
        }
        red.push(((x, y), z));
    }
    for _ in 0..n {
        let (x, y) = read_tuple();
        let mut z = 0;
        if x > y {
            z = y.clone();
        } else {
            z = x.clone();
        }
        blue.push(((x, y), z));
    }

    println!("{}", solve(red, blue));
}

fn solve(mut red: Vec<((u32, u32), u32)>, mut blue: Vec<((u32, u32), u32)>) -> u32 {
    red.sort_by(|a, b| b.1.cmp(&a.1));
    blue.sort_by(|a, b| b.1.cmp(&a.1));
    
    let mut cnt = 0;
    let ((mut a, mut b), _) = red.pop().unwrap();
    let ((mut c, mut d), _) = blue.pop().unwrap();

    loop {
        if a < c && b < d {
            cnt += 1;

            if red.is_empty() || blue.is_empty() {
                break
            }

            let ((e, f), _) = red.pop().unwrap();
            let ((g, h), _) = blue.pop().unwrap();
            a = e; b = f; c = g; d = h;
            continue;
        }

        if red.is_empty() || blue.is_empty() {
            break
        }

        let ((x, y), _) = blue.pop().unwrap();
        c = x; d = y;
    }

    cnt
}

#[test]
fn test1() {
    let red = vec![((2, 0), 0), ((3, 1), 1), ((1, 3), 1)];
    let blue = vec![((4, 2), 2), ((0, 4), 0), ((5, 5), 5)];
    assert_eq!(2, solve(red, blue));
}

#[test]
fn test2() {
    let red = vec![((0, 0), 0), ((1, 1), 1), ((5, 2), 2)];
    let blue = vec![((2, 3), 2), ((3, 4), 3), ((4, 5), 4)];
    assert_eq!(2, solve(red, blue));
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().parse().ok().unwrap()
}

fn read_tuple() -> (u32, u32) {
    let v = read_vec::<u32>();
    (v[0], v[1])
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().split_whitespace().map(|e| e.parse().ok().unwrap()).collect()
}