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::collections::HashSet;

fn main() {
  let nm = read_vec::<u32>();
  let n = nm[0];
  let m = nm[1];
  let mut inputs: HashSet<Vec<u32>> = HashSet::new();
  for _ in 0..n {
    let ab = read_vec::<u32>();
    if ab[0] <= m {
      inputs.insert(ab);
    }
  }

  let mut sum = 0;
  for j in 1..(m + 1) {
    let target = {
      let max = get_max(&inputs, j);
      match max {
        Some(a) => {
          sum += a[1];
          Some(a)
        }
        None => { None }
      }
    };
    match target {
      Some(a) => { inputs.remove(&a); }
      None => {}
    }
  }

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

fn get_max(inputs: &HashSet<Vec<u32>>, j: u32) -> Option<Vec<u32>> {
  match inputs.iter().filter(|a| a[0] <= j).max_by_key(|a| a[1]) {
    Some(a) => { Some(a.to_vec()) }
    None => { None }
  }
}


fn read<T: std::str::FromStr>() -> T {
  let mut s = String::new();
  std::io::stdin().read_line(&mut s).ok();
  s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
  read::<String>()
    .split_whitespace()
    .map(|e| e.parse().ok().unwrap())
    .collect()
}