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.ArrayList;
import java.util.Collections;
import java.util.PriorityQueue;
import java.util.Scanner;
 
public class Main {
 
	public static void main(String args[])
	{
		Scanner scan=new Scanner(System.in);
		int n=scan.nextInt();
		int m=scan.nextInt();
		ArrayList<Integer>[] adj=new ArrayList[100001];
		for(int i=0;i<=100000;i++)
		{
			adj[i]=new ArrayList<Integer>();
		}
		for(int i=0;i<n;i++)
		{
			int u=scan.nextInt();
			int v=scan.nextInt();
			adj[u].add(v);
		}
		long tot=0;
		PriorityQueue<Integer> que=new PriorityQueue<Integer>(Collections.reverseOrder());
		for(int i=1;i<=m;i++)
		{
			for(int x:adj[i])
			{
				que.add(x);
			}
			if(!que.isEmpty())
			{
				int q=que.poll();
//				System.out.println(q);
				tot+=q;
			}
		}
		System.out.println(tot);
	}
}