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.*;

public class Main {

  public static void main (String[] args) {

    Scanner sc = new Scanner(System.in);

    int N = sc.nextInt();
    int M = sc.nextInt();
    int[] A = new int[N]; 
    int[] B = new int[N];

    Data []d = new Data[N];

    for (int i = 0; i < N; i++) {
      A[i] = sc.nextInt();
      B[i] = sc.nextInt();
      d[i] = new Data(A[i], B[i]);
    }

    sc.close(); 

    Arrays.sort(d, new Comparator<Data>() {
      public int compare(Data d1, Data d2) {
          int t_ = d2.getA() - d1.getA();
          if (t_ == 0) {
            return d2.getB() - d1.getB();
          } else {
            return d2.getA() - d1.getA();
          }
      }
    });

    int day = 0;
    int sum  = 0;

    for(int i = 0; i < N; i++) {
        if (d[i].getA() <= M) {
          if (day != d[i].getA() || d[i].getA() == 1){
            day = d[i].getA();
            sum += d[i].getB();
            M--;
            if (M <= 0) {
              break;
            }
          }
        }
    }

    System.out.println(sum);
  
  }

  public static class Data{
    private int a;
    private int b;
    public Data(int a, int b) {
        this.a = a;
        this.b = b;
    }
    public int getA() {
        return a;
    }
    public int getB() {
        return b;
    }
  }

}