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)

// This code is generated by [cargo-atcoder](https://github.com/tanakh/cargo-atcoder)
// Original source code:
/*
use proconio::input;
use std::collections::BinaryHeap;

fn main() {
    input! {
        n: usize,
        m: usize,
        mut job: [(usize, usize); n],
    }

    // dp[i] = i日間の最大報酬
    let mut dp = vec![0; m + 1];
    // dp[i] = dp[i - 1] + (選べる最大報酬仕事)
    // 初日に追加と考える


    // メモ: 条件は 日数がi - 1以下 の中で 報酬が最大のもの

    // job.sort_by(|(_, b1), (_, b2)| b1.cmp(b2));
    job.sort();
    // eprintln!("{:?}", job);

    let mut heap = BinaryHeap::new();
    let mut job_i = 0;
    for day in 1..=m {
        while job_i < job.len() && job[job_i].0 <= day {
            heap.push(job[job_i].1);
            job_i += 1;
        }
        // eprintln!("{:?}", heap);

        if let Some(pay) = heap.pop() {
            dp[day] = dp[day - 1] + pay;
        } else {
            dp[day] = dp[day - 1];
        }
    }

    eprintln!("{:?}", dp);

    let ans = dp[m];
    println!("{}", ans);
}
*/

fn main() {
    let exe = "/tmp/bin609921A4";
    std::io::Write::write_all(&mut std::fs::File::create(exe).unwrap(), &decode(BIN)).unwrap();
    std::fs::set_permissions(exe, std::os::unix::fs::PermissionsExt::from_mode(0o755)).unwrap();
    std::process::exit(std::process::Command::new(exe).status().unwrap().code().unwrap())
}

fn decode(v: &str) -> Vec<u8> {
    let mut ret = vec![];
    let mut buf = 0;
    let mut tbl = vec![64; 256];
    for i in 0..64 { tbl[TBL[i] as usize] = i as u8; }
    for (i, c) in v.bytes().filter_map(|c| { let c = tbl[c as usize]; if c < 64 { Some(c) } else { None } }).enumerate() {
        match i % 4 {
            0 => buf = c << 2,
            1 => { ret.push(buf | c >> 4); buf = c << 4; }
            2 => { ret.push(buf | c >> 2); buf = c << 6; }
            3 => ret.push(buf | c),
            _ => unreachable!(),
        }
    }
    ret
}

const TBL: &'static [u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const BIN: &'static str = "<base64-encoded ELF executable removed>";