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.*;
import java.math.*;


public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();
        PriorityQueue<Pair> list = new PriorityQueue<Pair>((a,b)->{
          return a.a==b.a?b.b-a.b:a.a-b.a;
        });
        for(int i=0;i<N;i++){
          list.add(new Pair(sc.nextInt(),sc.nextInt()));
        }

        Pair el;
        int now = 0;
        int pre = -1;
        int cnt = 0;
        int cmax = 0;
        PriorityQueue<Integer> anses = new PriorityQueue<Integer>((a,b)->b-a);
        int ans = 0;
        for(int i=1;i<=M;i++){
          Pair p;
          while((p=list.poll()) != null){
            int a = p.a;
            int b = p.b;
            if(a<=i){
              anses.add(b);
            }else{
              list.add(p);
              break;
            }
          }
          if(!anses.isEmpty()){
            ans += anses.poll();
          }
        }
        System.out.println(ans);
    }
    private static class Pair{
      public int a, b;
      Pair(int a,int b){
        this.a = a;
        this.b = b;
      }
    }
}