Problem:
Score : 400 points

Problem Statement

There are N one-off jobs available. If you take the i-th job and complete it, you will earn the reward of B_i after A_i days from the day you do it.

You can take and complete at most one of these jobs in a day.

However, you cannot retake a job that you have already done.

Find the maximum total reward that you can earn no later than M days from today.

You can already start working today.

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq A_i \leq 10^5

1 \leq B_i \leq 10^4

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N

Output

Print the maximum total reward that you can earn no later than M days from today.

Sample Input 1

3 4
4 3
4 1
2 2

Sample Output 1

5

You can earn the total reward of 5 by taking the jobs as follows:

Take and complete the first job today. You will earn the reward of 3 after four days from today.

Take and complete the third job tomorrow. You will earn the reward of 2 after two days from tomorrow, that is, after three days from today.

Sample Input 2

5 3
1 2
1 3
1 4
2 1
2 3

Sample Output 2

10

Sample Input 3

1 1
2 1

Sample Output 3

0

Solution in Rust (1.15.1) (judge verdict: Runtime Error)

use std::io::{BufRead, Read};

pub struct Scanner<R>
where
    R: BufRead,
{
    reader: R,
}

impl<R> Scanner<R>
where
    R: BufRead,
{
    pub fn new(reader: R) -> Self {
        Scanner { reader: reader }
    }

    pub fn next<T>(&mut self) -> T
    where
        T: ::std::str::FromStr,
        <T as ::std::str::FromStr>::Err: ::std::fmt::Debug,
    {
        self.reader
            .by_ref()
            .bytes()
            .map(|b| b.unwrap() as char)
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect::<String>()
            .parse::<T>()
            .unwrap()
    }
}

use std::cmp::Ordering;

fn main() {
    let stdin = std::io::stdin();
    let stdin = stdin.lock();
    let mut sc = Scanner::new(stdin);

    let n: i64 = sc.next();
    let m: i64 = sc.next();
    let mut v: Vec<(i64, u64)> = (0..n).map(|_| (sc.next(), sc.next())).collect();

    v.sort_by(|a, b| match a.1.cmp(&b.1).reverse() {
        Ordering::Equal => a.0.cmp(&b.0).reverse(),
        order => order,
    });
    // println!("{:?}", v);

    let mut reword_sum: u64 = 0;

    for i in 0..m {
        for j in 0..v.len() {
            let (after, reword) = v[j as usize];
            if i + after <= m {
                reword_sum += reword;
                for k in 0..j + 1 {
                    v.remove(k);
                }
                break;
            }
        }
    }

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