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 (1.42.0) (judge verdict: Accepted)

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

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

/*
ここまでテンプレ
*/
fn ord(a: (i32, i32), b: (i32, i32)) -> bool {
    if (a.0 < b.0) {
        true
    } else {
        false
    }
}
const INF: i32 = 1 << 13;
fn main() {
    let N = read::<i32>();
    let mut Red: Vec<(i32, i32)> = vec![(0, 0); N as usize];
    let mut Blue: Vec<(i32, i32)> = vec![(0, 0); N as usize];
    for i in 0..N as usize {
        let tmp = read_vec::<i32>();
        Red[i] = (tmp[0], tmp[1]);
    }
    for i in 0..N as usize {
        let tmp = read_vec::<i32>();
        Blue[i] = (tmp[0], tmp[1]);
    }
    Blue.sort_unstable();
    //println!("{:?}", Blue);
    let mut ans: u32 = 0;
    for i in 0..N as usize {
        let mut id = -1;
        let mut num = -1;
        for j in 0..N as usize {
            if Red[j].1 < Blue[i].1 && Red[j].0 < Blue[i].0 {
                if num < Red[j].1 {
                    num = Red[j].1;
                    id = j as i32;
                }
            }
        }
        if id == -1 {
            continue;
        }
        ans += 1;
        Red[id as usize].0 = INF;
        Red[id as usize].1 = INF;
    }
    println!("{}", ans);
}