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)

#![allow(unused_imports, unused_variables, dead_code, non_snake_case, unused_macros)]
use std::io::{stdin, Read, StdinLock};
use std::str::FromStr;
use std::fmt::*;
use std::str::*;
use std::cmp::*;
use std::collections::*;
fn getline() -> String {
    let mut res = String::new();
    std::io::stdin().read_line(&mut res).ok();
    res
}
macro_rules ! readl { ( $ t : ty ) => { { let s = getline ( ) ; s . trim ( ) . parse ::<$ t > ( ) . unwrap ( ) } } ; ( $ ( $ t : ty ) ,+ ) => { { let s = getline ( ) ; let mut iter = s . trim ( ) . split ( ' ' ) ; ( $ ( iter . next ( ) . unwrap ( ) . parse ::<$ t > ( ) . unwrap ( ) , ) * ) } } ; }
macro_rules ! readlvec { ( $ t : ty ) => { { let s = getline ( ) ; let iter = s . trim ( ) . split ( ' ' ) ; iter . map ( | x | x . parse ( ) . unwrap ( ) ) . collect ::< Vec <$ t >> ( ) } } }
macro_rules ! mvec { ( $ v : expr , $ s : expr ) => { vec ! [ $ v ; $ s ] } ; ( $ v : expr , $ s : expr , $ ( $ t : expr ) ,* ) => { vec ! [ mvec ! ( $ v , $ ( $ t ) ,* ) ; $ s ] } ; }
macro_rules ! debug { ( $ x : expr ) => { println ! ( "{}: {:?}" , stringify ! ( $ x ) , $ x ) } }
fn printiter<'a, T>(v: &'a T)
where
    &'a T: std::iter::IntoIterator,
    <&'a T as std::iter::IntoIterator>::Item: std::fmt::Display,
{
    for (i, e) in v.into_iter().enumerate() {
        if i != 0 {
            print!(" ");
        }
        print!("{}", e);
    }
    println!("");
}
struct ContestPrinter {
    s: String,
}
impl ContestPrinter {
    fn new() -> ContestPrinter {
        ContestPrinter { s: String::new() }
    }
    fn print<T>(&mut self, x: T)
    where
        T: std::fmt::Display,
    {
        self.s.push_str(format!("{}", x).as_str());
    }
    fn println<T>(&mut self, x: T)
    where
        T: std::fmt::Display,
    {
        self.s.push_str(format!("{}\n", x).as_str());
    }
}
impl std::ops::Drop for ContestPrinter {
    fn drop(&mut self) {
        print!("{}", self.s);
    }
}
fn is_max_i64(num: i64) -> bool {
    if num == i64::max_value() {
        true
    } else {
        false
    }
}

fn main() {
    let mut pr = ContestPrinter::new();
    
    
    let N = readl!(usize);
    
    let mut ps = Vec::new();
    for i in 0..N {
        let (a, b) = readl!(i32, i32);
        ps.push((a, b, 1));
    }
    for i in 0..N {
        let (c, d) = readl!(i32, i32);
        ps.push((c, d, -1));
    }

    ps.sort();

    let mut ans = 0;
    let mut hs = HashSet::new();
    for p in ps {
        let (x, y, t) = p;
        if t == 1 {
            hs.insert((x, y));
        } else {
            let (mut maxx, mut maxy) = (-1, -1);
            for h in hs.iter() {
                let &(hx, hy) = h;
                if (hy < y) & (maxy < hy) {
                    maxx = h.0;
                    maxy = h.1;
                }
            }
            if maxx != -1 {
                hs.remove(&(maxx, maxy));
                ans += 1;
            }
        }
    }

    pr.println(ans);
}