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: Time Limit Exceeded)

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

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

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();

		Map<Integer,List<Integer>> map = new HashMap<>();

		for(int i = 0;i < n;i++) {
			int a = sc.nextInt();
			int b = sc.nextInt();

			List<Integer> arr = (map.containsKey(a)) ?
				map.get(a) : new ArrayList<>();

			arr.add(b);
			map.put(a, arr);
		}

		for (List<Integer> val : map.values()) {
			Collections.sort(val, Collections.reverseOrder());
		}

		int result = 0;
		for(int i = 1;i <= m;i++) {

			int workMax = 0;
			int key = 0;
			for(int j = i;j > 0;j--) {
				if(map.containsKey(j) && map.get(j).size() >= 1) {
					List<Integer> lis = map.get(j);

					if(workMax <= lis.get(0)) {
						workMax =lis.get(0);
						key = j;
					}
				}
			}

			if(key != 0) {
				List<Integer> lis = map.get(key);
				lis.remove(0);
			}
			result += workMax;
		}

		System.out.println(result);
	}
}