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: Accepted)

import java.util.*;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        Job[] jobs = new Job[n];
        PriorityQueue<Integer> queue = new PriorityQueue<>(Collections.reverseOrder());
        for(int i = 0; i<n; i++) jobs[i] = new Job(sc.nextInt(), sc.nextInt());

        Arrays.sort(jobs, (ac, bc)->(ac.a - bc.a));
        long cnt = 1;
        long ans = 0;
        for(int i = 0; i<n; i++) {
            if(jobs[i].a == cnt) queue.add(jobs[i].b);
            else {
                while(jobs[i].a != cnt && cnt<=m) {
                    if (queue.size() != 0) ans += (long)queue.poll();
                    System.err.println("ans = " +cnt+" "+ ans);
                    cnt++;
                }
                queue.add(jobs[i].b);
            }
        }
        //System.err.println("day = " + cnt);
        while(cnt<=m && queue.size()!=0) {
            ans+= (long)queue.poll();
            System.err.println("ans = " + ans);
            cnt++;
        }

        System.out.println(ans);

    }
}
class Job {
    int a,b;
    public Job(int a, int b) {
        this.a = a;
        this.b = b;
    }
}