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.io.PrintWriter;
import java.util.*;

public class Main {

    private static Scanner in = new Scanner(System.in);
    private static PrintWriter out = new PrintWriter(System.out);

    private static final long MOD = (long) 1e9 + 7;

    public static void main(String[] args) {
        solve();
        out.flush();
    }

    private static void solve() {
        int n = in.nextInt();
        int m = in.nextInt();

        long ans = 0;
        Map<Integer, List<Map.Entry<Integer, Integer>>> arbeits = new HashMap<>();
        for (int i=0; i < n; i++) {
            int a = in.nextInt();
            int b = in.nextInt();
            if (!arbeits.containsKey(a))
                arbeits.put(a, new ArrayList<>());
            arbeits.get(a).add(new AbstractMap.SimpleEntry<>(a, b));
        }

        arbeits.entrySet().forEach(e -> e.getValue().sort(((o1, o2) -> o2.getValue() - o1.getValue())));

        PriorityQueue<Map.Entry<Integer, Integer>> available = new PriorityQueue<>(new Comparator<Map.Entry<Integer, Integer>>() {
            @Override
            public int compare(Map.Entry<Integer, Integer> o1, Map.Entry<Integer, Integer> o2) {
                return o2.getValue() - o1.getValue();
            }
        });
        for (int i=1; i <= m; i++) {
            available.addAll(arbeits.getOrDefault(i, new ArrayList<>()));
            if (available.size() != 0) {
                ans += available.poll().getValue();
            }
        }
        out.println(ans);
    }

    private static class Arbeit {
        int a;
        int b;
        public Arbeit(int a, int b) {
            this.a = a;
            this.b = b;
        }

        @Override
        public boolean equals(Object obj) {
            return obj instanceof Arbeit && ((Arbeit) obj).a == this.a && ((Arbeit) obj).b == this.b;
        }

        @Override
        public int hashCode() {
            return super.hashCode();
        }
    }

}