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::io;
use std::cmp;
use std::collections::BinaryHeap;


fn main() {
    let (n, m) = {
        let i = read::<usize>();
        (i[0], i[1])
    };
    let mut ab = Vec::new();
    for _ in 0..n {
        let (a, b) = {
            let i = read::<usize>();
            (i[0], i[1])
        };
        ab.push((a, b));
    }
    ab.sort_by(|x, y| (y.0).cmp(&x.0));
    // println!("{:?}", ab);

    let mut que = BinaryHeap::new();
    let mut ans: usize = 0;
    let mut idx = 0;
    let mut i = 0;

    while i < m {
        i += 1;
        for j in idx..n {
            if ab[n - j - 1].0 <= cmp::min(m, i) { que.push(ab[n - j - 1].1); }
            else { break; }
            idx = j + 1;
        }
        if let Some(b) = que.pop() {
            ans += b;
        }
    }
    println!("{}", ans);
}


#[allow(dead_code)]
fn read<T>() -> Vec<T>
where T:
std::str::FromStr,
T::Err: std::fmt::Debug {

    let mut buf = String::new();
    io::stdin().read_line(&mut buf).unwrap();
    buf.split_whitespace()
        .map(|s| s.trim().parse().unwrap())
        .collect()
}

#[allow(dead_code)]
fn read_one<T>() -> T
where T:
std::str::FromStr,
T::Err: std::fmt::Debug {

    let mut buf = String::new();
    io::stdin().read_line(&mut buf).unwrap();
    buf.trim().parse().unwrap()
}