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 (1.42.0) (judge verdict: Accepted)

#![allow(unused_imports)]

use proconio::{input, fastout};
use proconio::marker::*;
use smallvec::alloc::collections::BinaryHeap;

#[fastout]
fn main() {
    input! {
    n: usize,
    m: usize,
    mut ab: [(usize, usize); n]
    }
    let mut d: Vec<Vec<usize>> = vec![vec![]; m + 1];
    for i in 0..n {
        let (a, b) = ab[i];
        if a > m { continue; }
        d[a].push(b);
    }
    let mut q = BinaryHeap::new();
    let mut ans = 0;
    for i in 1..=m {
        for &j in &d[i] {
            q.push((j, i))
        }
        if let Some(x) = q.pop() {
            ans += x.0;
        }
    }
    println!("{}", ans);
}