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.*;
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[] anses = new int[M*2];
        while ((el = list.poll()) != null){
          int a = el.a;
          int b = el.b;
          if(pre == a)cnt++;
          else cnt = 0;
          if(now <= a){
            for(int i=0;a+i<=M;i++){
              if(anses[a+i] < b){
                for(int j=a+i+1;j<=M;j++){
                  anses[j] = anses[j-1];
                  if(anses[j] == 0)break;
                }
                anses[a+i] = b;
                break;
              }
            }
          }
          pre = a;
        }
        int ans = 0;
        for(int i=0;i<=M;i++){
          ans += anses[i];
        }

        System.out.println(ans);

    }
    private static class Pair{
      public int a, b;
      Pair(int a,int b){
        this.a = a;
        this.b = b;
      }
    }
}