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: Accepted)

use std::ops;

fn read_line() -> String {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim_right().to_owned()
}

fn read_stdin() -> String {
    use std::io::Read;
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    s
}

fn new_jobs() -> Vec<Vec<u64>> {
    let jobs = read_stdin().lines()
        .map(|line: &str| line.split_whitespace().map(|s| s.parse().unwrap()).collect())
        .collect::<Vec<Vec<u64>>>();
    
    let mut v = vec![Vec::new(); 100_000];
    for job in jobs {
        v[(job[0] - 1) as usize].push(job[1]);
    }
    v
}

trait Sorted {
    fn position_quick(&self, n: u64, range: ops::Range<usize>) -> usize;
    fn sorted_insert(&mut self, n: u64);
}

impl Sorted for Vec<u64> {
    fn position_quick(&self, n: u64, range: ops::Range<usize>) -> usize {
        let len = range.end - range.start;
        let i = range.start + len / 2;
        
        if len == 1 {
            return i + (self[i] < n) as usize;
        }
        
        if n < self[i] {
            self.position_quick(n, range.start..i)
        } else {
            self.position_quick(n, i..range.end)
        }
    }
    
    fn sorted_insert(&mut self, n: u64) {
        if self.is_empty() {
            self.push(n);
            return;
        }
        
        let i = self.position_quick(n, 0..self.len());
        self.insert(i, n);
    }
}

fn main() {
    let nums: Vec<usize> = read_line().split_whitespace().map(|x| x.parse().unwrap()).collect();
    let (_, m) = (nums[0], nums[1]);
    let jobs = new_jobs();
    
    let mut current = Vec::new();

    let mut total = 0;
    for day in 0..m {
        for &reward in &jobs[day] {
            current.sorted_insert(reward);
        }
        
        if current.is_empty() { continue; }
        
        let index = current.len() - 1;
        total += current[index];
        current.swap_remove(index);
    }
    
    println!("{}", total);
}