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::str::FromStr;
use std::fmt::Debug;
use std::cmp;
use std::collections::{BinaryHeap, VecDeque};


#[allow(dead_code)]
fn read_as_vec<T>() -> Vec<T>
where T: FromStr, <T as FromStr>::Err : Debug{
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().split_whitespace().map(|c| T::from_str(c).unwrap()).collect()

}

#[allow(dead_code)]
fn read_as_string() -> String{
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().to_string()
}

fn main(){
    let line = read_as_vec::<usize>();
    let (n, m) = (line[0], line[1]);

    let mut work_vec: Vec<(usize, usize)> = Vec::new();
    let mut heap = BinaryHeap::new();


    for _ in 0..n{
        let line = read_as_vec();
        work_vec.push((line[0], line[1]));
    }


    let mut sum_payment: usize = 0;
    //println!("{:?}", work_vec);
    work_vec.sort();
    work_vec.reverse();
    //println!("{:?}", work_vec);

    for i in 1..m+1{
        while work_vec.len() > 0 && work_vec.last().unwrap().0 <= i{
            heap.push(work_vec.pop().unwrap().1);
        }

        if let Some(payment) = heap.pop(){
            sum_payment += payment;
        }
    }

    println!("{:?}", sum_payment);
    //for work in work_vec{
    //}
}