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(unknown_lints)]
#![allow(unused_imports)]
#![allow(dead_code)]
#![allow(unused_macros)]
#![allow(non_snake_case)]
#![allow(bare_trait_objects)]

use std::cmp::{max, min};
use std::cmp::Ordering::{self, Equal, Greater, Less};
use std::collections::{HashMap, HashSet, VecDeque};
use std::f64::consts::PI;
use std::io::Write;
use std::ops::{AddAssign, Sub, Deref};
use std::borrow::Borrow;
use std::iter::FromIterator;

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

const DIRECTIONS: [(i32, i32); 4] = [(0, 1), (1, 0), (0, -1), (-1, 0)];

trait Ext {
    type Item;

    fn lower_bound(&self, x: &Self::Item) -> usize
        where
            Self::Item: Ord;

    fn lower_bound_by<'a, F>(&'a self, f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> Ordering;

    fn lower_bound_by_key<'a, K, F>(&'a self, k: &K, f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> K,
            K: Ord;

    fn upper_bound(&self, x: &Self::Item) -> usize
        where
            Self::Item: Ord;

    fn upper_bound_by<'a, F>(&'a self, f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> Ordering;

    fn upper_bound_by_key<'a, K, F>(&'a self, k: &K, f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> K,
            K: Ord;

    fn equal_range(&self, x: &Self::Item) -> std::ops::Range<usize>
        where
            Self::Item: Ord;

    fn equal_range_by<'a, F>(&'a self, f: F) -> std::ops::Range<usize>
        where
            F: FnMut(&'a Self::Item) -> Ordering;

    fn equal_range_by_key<'a, K, F>(&'a self, k: &K, f: F) -> std::ops::Range<usize>
        where
            F: FnMut(&'a Self::Item) -> K,
            K: Ord;
}

impl<T> Ext for [T] {
    type Item = T;

    fn lower_bound(&self, x: &Self::Item) -> usize
        where
            T: Ord,
    {
        self.lower_bound_by(|y| y.cmp(x))
    }
    fn lower_bound_by<'a, F>(&'a self, mut f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> Ordering,
    {
        let s = self;
        let mut size = s.len();
        if size == 0 {
            return 0;
        }
        let mut base = 0usize;
        while size > 1 {
            let half = size / 2;
            let mid = base + half;
            let cmp = f(unsafe { s.get_unchecked(mid) });
            base = if cmp == Less { mid } else { base };
            size -= half;
        }
        let cmp = f(unsafe { s.get_unchecked(base) });
        base + (cmp == Less) as usize
    }
    fn lower_bound_by_key<'a, K, F>(&'a self, k: &K, mut f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> K,
            K: Ord,
    {
        self.lower_bound_by(|e| f(e).cmp(k))
    }

    fn upper_bound(&self, x: &Self::Item) -> usize
        where
            T: Ord,
    {
        self.upper_bound_by(|y| y.cmp(x))
    }

    fn upper_bound_by<'a, F>(&'a self, mut f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> Ordering,
    {
        let s = self;
        let mut size = s.len();
        if size == 0 {
            return 0;
        }
        let mut base = 0usize;
        while size > 1 {
            let half = size / 2;
            let mid = base + half;
            let cmp = f(unsafe { s.get_unchecked(mid) });
            base = if cmp == Greater { base } else { mid };
            size -= half;
        }
        let cmp = f(unsafe { s.get_unchecked(base) });
        base + (cmp != Greater) as usize
    }
    fn upper_bound_by_key<'a, K, F>(&'a self, k: &K, mut f: F) -> usize
        where
            F: FnMut(&'a Self::Item) -> K,
            K: Ord,
    {
        self.upper_bound_by(|e| f(e).cmp(k))
    }

    fn equal_range(&self, x: &Self::Item) -> std::ops::Range<usize>
        where
            T: Ord,
    {
        self.equal_range_by(|y| y.cmp(x))
    }
    fn equal_range_by<'a, F>(&'a self, mut f: F) -> std::ops::Range<usize>
        where
            F: FnMut(&'a Self::Item) -> Ordering,
    {
        let s = self;
        let mut size = s.len();
        if size == 0 {
            return 0..0;
        }
        let mut base = (0usize, 0usize);
        while size > 1 {
            let half = size / 2;
            let mid = (base.0 + half, base.1 + half);
            let cmp = (
                f(unsafe { s.get_unchecked(mid.0) }),
                f(unsafe { s.get_unchecked(mid.1) }),
            );
            base = (
                if cmp.0 == Less { mid.0 } else { base.0 },
                if cmp.1 == Greater { base.1 } else { mid.1 },
            );
            size -= half;
        }
        let cmp = (
            f(unsafe { s.get_unchecked(base.0) }),
            f(unsafe { s.get_unchecked(base.1) }),
        );
        (base.0 + (cmp.0 == Less) as usize..base.1 + (cmp.1 != Greater) as usize)
    }

    fn equal_range_by_key<'a, K, F>(&'a self, k: &K, mut f: F) -> std::ops::Range<usize>
        where
            F: FnMut(&'a Self::Item) -> K,
            K: Ord,
    {
        self.equal_range_by(|e| f(e).cmp(k))
    }
}

struct UnionFind {
    parts: Vec<usize>
}

impl UnionFind {
    fn new(n: usize) -> UnionFind {
        let parts = (0..n).collect();
        UnionFind { parts: parts }
    }

    fn union(&mut self, i: usize, j: usize) {
        let i_leader = self.find(i);
        let j_leader = self.find(j);
        self.parts[j_leader] = self.parts[i_leader];
    }

    fn find(&mut self, i: usize) -> usize {
        let mut p = i;
        while self.parts[p] != p {
            p = self.parts[p]
        };
        let mut s = i;
        while s != p {
            let t = self.parts[s];
            self.parts[s] = p;
            s = t
        };
        p
    }

    fn find_only(&self, i: usize) -> usize {
        let mut p = i;
        while self.parts[p] != p {
            p = self.parts[p]
        };
        p
    }

    fn same(&mut self, i: usize, j: usize) -> bool {
        self.find(i) == self.find(j)
    }

    fn same_only(&self, i: usize, j: usize) -> bool {
        self.find_only(i) == self.find_only(j)
    }
}

enum Ops {
    Sum,
    Max,
}

struct BinaryIndexTree<T> {
    data: Vec<T>,
    ops: Ops,
}

impl<T> BinaryIndexTree<T>
    where
        T: Copy + AddAssign + Sub<Output=T> + Default + Ord,
{
    fn new(size: usize, ops: Ops) -> Self {
        let buf_size = size.next_power_of_two();
        BinaryIndexTree {
            data: vec![T::default(); buf_size + 1],
            ops: ops,
        }
    }

    fn query(&self, i: usize) -> T {
        let mut i = i as i64;
        let mut ret = T::default();
        match self.ops {
            Ops::Sum => {
                while i > 0 {
                    ret += self.data[i as usize];
                    i -= i & -i;
                }
            }
            Ops::Max => {
                while i > 0 {
                    ret = max(ret, self.data[i as usize]);
                    i -= i & -i;
                }
            }
        }
        ret
    }

    fn set(&mut self, i: usize, value: T) {
        assert!(i > 0);
        let n = self.data.len() as i64;
        let mut i = i as i64;
        match self.ops {
            Ops::Sum => {
                while i <= n - 1 {
                    self.data[i as usize] += value;
                    i += i & -i;
                }
            }
            Ops::Max => {
                while i <= n - 1 && self.data[i as usize] < value {
                    self.data[i as usize] = value;
                    i += i & -i;
                }
            }
        }
    }
}

fn clamp<T: PartialOrd>(input: T, min: T, max: T) -> T {
    debug_assert!(min <= max, "min must be less than or equal to max");
    if input < min {
        min
    } else if input > max {
        max
    } else {
        input
    }
}

fn coord_compress<T: std::clone::Clone + std::cmp::Ord>(src: Vec<T>) -> Vec<usize> {
    let mut tmp = src.clone();
    tmp.sort();
    tmp.dedup();
    src.iter()
        .map(|x| {
            tmp.binary_search(x).unwrap()
        })
        .collect()
}

fn binary_search<F>(l: i64, r: i64, query_fn: F) -> i64 where F: Fn(i64) -> bool {
    let mut size = r - l;
    let mut base = l;
    while size > 1 {
        let half = size / 2;
        let mid = base + half;
        if !query_fn(mid) {
            base = mid;
        }
        size -= half;
    }
    base + !query_fn(base) as i64
}

fn rel<T: PartialOrd + Default>(n: T) -> T {
    if n < T::default() {
        T::default()
    } else {
        n
    }
}

fn rem_euclid(a: i64, rhs: i64) -> i64 {
    let r = a % rhs;
    if r < 0 {
        if rhs < 0 {
            r - rhs
        } else {
            r + rhs
        }
    } else {
        r
    }
}

fn div_euclid(a: i64, rhs: i64) -> i64 {
    let q = a / rhs;
    if a % rhs < 0 {
        return if rhs > 0 { q - 1 } else { q + 1 };
    }
    q
}

fn permutations(n: usize, k: usize) -> Box<Iterator<Item=Vec<u8>>> {
    fn inner(array: Vec<u8>, depth: usize, max: u8) -> Box<Iterator<Item=Vec<u8>>> {
        let na = (0..max).flat_map(move |x| {
            if array.contains(&x) {
                None
            } else {
                let mut newarray = array.clone();
                newarray.push(x);
                Some(newarray)
            }
        });
        if depth > 0 {
            Box::new(na.flat_map(move |x| inner(x, depth - 1, max)))
        } else {
            Box::new(na)
        }
    }
    inner(Vec::new(), k - 1, n as u8)
}

#[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)]
struct Reverse<T>(T);

impl<T: PartialOrd> PartialOrd for Reverse<T> {
    fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
        other.0.partial_cmp(&self.0)
    }
    fn lt(&self, other: &Self) -> bool { other.0 < self.0 }
    fn le(&self, other: &Self) -> bool { other.0 <= self.0 }
    fn gt(&self, other: &Self) -> bool { other.0 > self.0 }
    fn ge(&self, other: &Self) -> bool { other.0 >= self.0 }
}

impl<T: Ord> Ord for Reverse<T> {
    fn cmp(&self, other: &Reverse<T>) -> Ordering {
        other.0.cmp(&self.0)
    }
}

fn main() {
    input! {
        N: usize,
        aa: [(isize, isize); N],
        bb: [(isize, isize); N],
    }
    let mut aa: Vec<(isize, isize)> = aa;
    let mut bb: Vec<(isize, isize)> = bb;
//    debug!(N, aa, bb);

    bb.sort_by_key(|b| b.0);

    let mut res = 0;
    for (bx, by) in bb {
        let cc = aa.clone();
        let mut cc = cc.iter()
            .enumerate()
            .filter(|&(_idx, &(cx, cy))| {
                cx < bx && cy < by
            })
            .collect::<Vec<_>>();
        if cc.is_empty() { continue; }

        cc.sort_by_key(|&(_idx, &(_x, y))| -y);
        let idx = cc[0].0;

        aa.remove(idx);
        res += 1;
    }

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