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 libprocon::*;
use std::cmp::Ordering;
use std::collections::{HashMap, VecDeque};

fn main() {
    input! {
        N: usize,
        M: usize,
        AB: [(usize, usize); N],
    }
    // とりあえずソートしておく
    // Aについての降順、Aが等しい場合はBについての降順、とする
    let mut AB = AB;
    AB.sort_by(|x, y| match y.0.cmp(&x.0) {
        Ordering::Equal => y.1.cmp(&x.1),
        other => other,
    });
    // dbg!(&AB);

    // 方針
    // 最終日の1日前から順にさかのぼりながら考える
    // 最終日の1日前では、1日後に報酬がもらえるバイトのうち、一番報酬が高いものをやればOK
    // 最終日の2日前では、1日後or2日後に報酬がもらえるバイトのうち、一番報酬が高いものをやればOK. ただし、最終日1日前にやったバイトはやることができないことに注意
    // 以下同じように、貪欲にバイトを選択していけばよい。
    //
    // keyが「何日後に報酬がもらえるか」、valueがバイトの報酬のVec(降順）、となるようなHashMapを作る
    // また、セグメント木を作り、1日後、2日後、...、i日後に報酬がもらえるバイトのうち、一番報酬が高いものはどれか、というクエリをlogオーダーで解決できるようにしておく
    // これで O(nlogn) で解答できる はず。。。
    let mut hm = HashMap::with_capacity(N);
    let mut st = SegmentTree::new((0, 0), 100_000 + 1, |x, y| {
        if x.0 >= y.0 {
            (x.0, x.1)
        } else {
            (y.0, y.1)
        }
    });
    for (day, compensation) in AB.into_iter() {
        if !hm.contains_key(&day) {
            st.update(day, (compensation, day));
        }
        let entry = hm.entry(day).or_insert(VecDeque::new());
        entry.push_back(compensation);
    }

    // dbg!((
    //     st.query(1, 2),
    //     st.query(1, 3),
    //     st.query(1, 4),
    //     st.query(1, 5)
    // ));

    let mut ans = 0;
    for i in 1..=M {
        let res = st.query(1, i + 1);
        ans += res.0;
        if let Some(hm_el) = hm.get_mut(&res.1) {
            hm_el.pop_front();
            let next = hm.get(&res.1).unwrap().get(0).unwrap_or(&0);
            st.update(res.1, (*next, res.1));
        }
    }
    println!("{}", ans);
}
*/

fn main() {
    let exe = "/tmp/bin77611220";
    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>";