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::collections::BTreeSet;

fn read_line() -> String {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().to_owned()
}

fn reads<T>() -> Vec<T>
where
    T: std::str::FromStr,
    <T as std::str::FromStr>::Err: std::fmt::Debug,
{
    read_line()
        .split_whitespace()
        .map(|w| w.parse().unwrap())
        .collect()
}

fn main() {
    let n = reads()[0];

    let mut rs: Vec<(i32, i32)> = (0..n)
        .map(|_| {
            let v = reads();
            (v[0], v[1])
        })
        .collect();

    let mut bs: Vec<(i32, i32)> = (0..n)
        .map(|_| {
            let v = reads();
            (v[0], v[1])
        })
        .collect();

    rs.sort();
    bs.sort();

    let mut ys = BTreeSet::<i32>::new();
    let mut ri = 0;
    let mut ans = 0;

    for &(bx, by) in bs.iter() {
        while ri < rs.len() && rs[ri].0 < bx {
            ys.insert(rs[ri].1);
            ri += 1;
        }

        let mut cand = -1;
        for &y in ys.iter() {
            if y < by && y > cand {
                cand = y;
            }
        }

        if cand >= 0 {
            ans += 1;
            ys.remove(&cand);
        }
    }

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