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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int numberOfJobs = scanner.nextInt();
        int remainingDays = scanner.nextInt();
        List<JobInfo> pairs = new ArrayList<>();
        for (int i = 0; i < numberOfJobs; i++) {
            int days = scanner.nextInt();
            int reward = scanner.nextInt();
            if (days <= remainingDays)
                pairs.add(new JobInfo(days, reward));
        }
        int size = 1;
        long totalReward = 0;

        pairs.sort(Comparator.comparingInt(a -> a.days));
        PriorityQueue<JobInfo> priorityQueue = new PriorityQueue<>(Comparator.comparingInt(a -> -a.reward));
        while (size <= remainingDays) {
            for (int i = 0; i < pairs.size(); i++) {
                JobInfo info = pairs.get(i);
                if (info.days <= size) {
                    priorityQueue.add(info);
                    pairs.remove(info);
                } else break;
            }
            if (!priorityQueue.isEmpty()) totalReward += priorityQueue.poll().reward;
            size++;
        }
        System.out.println(totalReward);
    }

    private static class JobInfo {
        int days;
        int reward;

        public JobInfo(int days, int reward) {
            this.days = days;
            this.reward = reward;
        }
    }
}