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.List;
import java.util.Scanner;

public class Main {
	public static void main(String[] args){

		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		int m = sc.nextInt();

		List<Job> jobs = new ArrayList<>();


		//double temp =0;
		//List<Double> list = new ArrayList<>();
		for(int i=0;i<n;i++) {
			Job job = new Job(sc.nextInt(),sc.nextInt());
			jobs.add(job);
		}

		jobs.sort((a,b) -> a.day-b.day);

		int score = 0;

		int[] list = new int[10001];
		for(int i=0;i<10001;i++) {
			list[i]=0;
		}
		int biggestEarn = 0;
		int jobIndex = 0;
		
		
		for(int i = 1;i<m+1;i++) {
			while(jobs.size()>jobIndex) {
					if(jobs.get(jobIndex).day==i) {
						list[jobs.get(jobIndex).money]+=1;
						if(biggestEarn<jobs.get(jobIndex).money) {
							biggestEarn=jobs.get(jobIndex).money;
						}
						jobIndex++;
						
					}else {
						break;
					}

			}

			if(biggestEarn>0) {
				score += biggestEarn;
				list[biggestEarn]-=1;
				if(list[biggestEarn]==0) {
					while(biggestEarn!=0) {
						biggestEarn-=1;
						if(list[biggestEarn]!=0) {
							break;
						}
					}
				}
			}

		}
		System.out.println(score);
	}

}

class Job{
	int day;
	int money;
	Job(int day, int money){
		this.day = day;
		this.money = money;
	}
}