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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main{
	public static void main(String[] args) throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] line = br.readLine().split(" ");
		int n = Integer.parseInt(line[0]);
		int m = Integer.parseInt(line[1]);
		int i, j;
		Job[] jobs = new Job[n];
		for(i=0; i<n; i++)
			jobs[i] = new Job(br.readLine());
		
		//sort
		Job tmp;
		for(i=0; i<n-1; i++) for(j=i; j<n; j++) if( jobs[i].compareTo(jobs[j]) < 0 ){
			tmp = jobs[i];
			jobs[i] = jobs[j];
			jobs[j] = tmp;
		}
		
		int now = 0;
		int result = 0;
		for(i=0; i<n; i++) if( jobs[i].receive <= m-now ){
			now++;
			result += jobs[i].reward;
		}
		
		System.out.println(result);
	}
	
	public static class Job implements Comparable<Job>{
		public int receive, reward;
		
		public Job(String str){
			String[] line = str.split(" ");
			this.receive = Integer.parseInt(line[0]);
			this.reward = Integer.parseInt(line[1]);
		}

		@Override
		public int compareTo(Job other){
			if( this.reward < other.reward )
				return -1;
			else if( other.reward < this.reward )
				return 1;
			else if( this.receive < other.receive )
				return -1;
			else if( other.receive < this.receive )
				return 1;
			
			return 0;
		}
	}
}