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

public class Main {

	public static void main(String[] args) {

		Main main = new Main();
		main.exec();

	}

	private void exec() {
		int n;
		int m;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		m = sc.nextInt();
		int[] mValue = new int[n];
		List<Task> taskList = new ArrayList<>();
		for(int i = 0 ; i < n ; i++) {
			taskList.add(new Task(sc.nextInt(), sc.nextInt()));
		}
		Collections.sort(taskList);
		for(Task task : taskList) {
			// 一番うしろの日
			int lastIndex = m - task.day;
			for(int i = lastIndex ; i >= 0 ; i--) {
				if(mValue[i] == 0) {
					mValue[i] = task.value;
					break;
				}
			}
		}
		int sum = 0;
		for(int value : mValue) {
			sum += value;
		}
		System.out.println(sum);
		sc.close();
	}

	class Task implements Comparable<Task> {
		public int value;
		public int day;
		public Task(int day, int value) {
			this.value = value;
			this.day = day;
		}
		@Override
		public int compareTo(Task o) {
			if(o.value == value) {
				return day - o.day;
			}
			return o.value - value;
		}

	}
}