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::collections::{BinaryHeap, HashMap};
use std::io::Read;



fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();
    let mut iter = buf.split_whitespace();
    let n: i32 = iter.next().unwrap().parse().unwrap();
    let m: i32 = iter.next().unwrap().parse().unwrap();
    let mut jobs:HashMap<i32, Vec<i32> > = HashMap::new();
    let mut available_jobs:BinaryHeap<i32> = BinaryHeap::new();
    
    for _ in 0..n{    
        let a:i32 = iter.next().unwrap().parse().unwrap();
        let b:i32 = iter.next().unwrap().parse().unwrap();
        let etry = jobs.entry(a).or_insert(vec![]);
        etry.push(b);
    }

    let mut ans = 0i32;
    for day in 1..m+1{
        let entr = jobs.entry(day).or_insert(vec![]);
        for j in entr{
            available_jobs.push(*j);
        }
        if let Some(&x) = available_jobs.peek(){
            ans += x;
            available_jobs.pop();
        }
    }
    println!("{}", ans);
}