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.*;
 
public class Main{
  public static void main(String[]args){
    Scanner sc =  new Scanner(System.in);
    String[] S = sc.nextLine().split(" ");
    int N = Integer.parseInt(S[0]);
    int M = Integer.parseInt(S[1]);
    
    int[][] val = new int[N][2];
    for(int i = 0; i < N; i++){
      String[] t = sc.nextLine().split(" ");
      val[i][0] = Integer.parseInt(t[0]);
      val[i][1] = Integer.parseInt(t[1]);
    }
    Arrays.sort(val, (a, b) -> Integer.compare(a[0], b[0]));
    
    Queue<Integer> pq = new PriorityQueue<>(Collections.reverseOrder());
    int ans = 0;
    int A = 0;
    for(int i = 1; i <= M; i++){
      while(A < N && val[A][0] <= i){
        pq.offer(val[A][1]);
        A++;
      }
      if(!pq.isEmpty()){
      	ans += pq.poll();
      }
    }
    System.out.println(ans);
  }
}