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: Wrong Answer)

use std::io;
use std::io::BufRead;
use std::cmp::Ordering;

fn main() {
    let stdin = io::stdin();
    let mut stdin = stdin.lock();
    
    let (n, m) = {
        let mut n = String::new();
        stdin.read_line(&mut n).unwrap();
        let mut input = n.trim().split_whitespace();
        (
            input.next().unwrap().parse::<usize>().unwrap(),
            input.next().unwrap().parse::<i32>().unwrap(),
        )
    };

    let mut work = Vec::with_capacity(n);
    for _ in 0..n {
        let mut n = String::new();
        stdin.read_line(&mut n).unwrap();
        let mut input = n.trim().split_whitespace();
        let a = input.next().unwrap().parse::<i32>().unwrap();
        let b = input.next().unwrap().parse::<i32>().unwrap();
        if a <= m {
            work.push((a,b));
        }// else { eprintln!("do not use {} {} | m = {}", a, b, m ); }
    }
    work.sort_by(|a, b| match a.0.cmp(&b.0) {
        Ordering::Equal => { a.1.cmp(&b.1) },
        Ordering::Less  => Ordering::Less,
        Ordering::Greater => Ordering::Greater,
    });

    let mut gain: i32 = 0;

    for i in (0..m).rev() {
        //eprintln!("{} {:?}", i, work);
        
        let mut target = 0;
        let mut max = 0;
        for (i,&(a,b)) in work.iter().enumerate() {
            if b+a >= max { max = b+a; target = i; }
        }
        if max == 0 { break; }
        
         gain += work.remove(target).1;
        
        loop {
            match work.last() {
                None => { break; }
                Some(&(a,_)) => {
                    if a > i { work.pop().unwrap(); } else { break; }
                },
            }
        }
    }

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