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: Runtime Error)

import java.util.Scanner;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class Main{
  public static void main(String[] args){
    Scanner s = new Scanner(System.in);
    int Ans = 0;
    int N = s.nextInt();
    int M = s.nextInt();
    ArrayList<Integer> A = new ArrayList<Integer>();
    for (int i = 0; i < N; i++){
      A.add(s.nextInt() + s.nextInt()* 10000 );
    }
    Collections.sort(A,Comparator.reverseOrder());
    int j = 0;
    for (int i = M;i>=0;i--){
      if (A.size() != 0){
        while (A.get(j) % 10000 + i > M) {
          j++;
          if (j >= A.size()-1){
            A.add(0);
            j = A.size()-1;
            break;
          }
        }
      }
      Ans += A.get(j)/10000;
      A.remove(j);
      j = 0;
    }
    System.out.println(Ans);
  }
}