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::io;
use std::str::FromStr;
use std::collections::VecDeque;

type Point = (i32, i32);

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

fn input_int_tuple() -> (i32, i32) {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line);
    let vec: Vec<i32> = line.split_whitespace().map(|s| s.parse().unwrap()).collect();
    (vec[0], vec[1])
}

fn main() {
    let n: i32 = input();
    let mut red_vec: Vec<Point> = Vec::new();
    for i in 0..n {
        let point: Point = input_int_tuple();
        red_vec.push(point);
    }
    red_vec.sort_by(|n, m| m.0.cmp(&n.0));

    let mut blue_vec: Vec<Point> = Vec::new();
    for i in 0..n {
        let point: Point = input_int_tuple();
        blue_vec.push(point);
    }
    blue_vec.sort_by(|n, m| n.0.cmp(&m.0));

    let mut count = 0;
    for red in red_vec {
        let mut idx: usize = 1000;
        for i in 0..blue_vec.len() {
            if blue_vec[i].0 > red.0 {
                idx = i as usize;
                break;
            }
        }
        if idx == 1000 {
            continue;
        }
        let mut min = 1000;
        let mut min_idx = 0;

        for i in idx..blue_vec.len() {
            if blue_vec[i].1 > red.1 {
                if blue_vec[i].1 < min {
                    min_idx = i;
                    min = blue_vec[i].1;
                }
            }
        }
        if min != 1000 {
            count += 1;   
            blue_vec.remove(min_idx);
        }
    }
    println!("{}", count);
}