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.*;
import java.io.*;
import static java.lang.Math.*;
import java.math.BigInteger;

public class Main {

    public static void main(String[] args) throws Exception {
        FastScanner scanner = new FastScanner();
        int n, m;
        int[] tmp = scanner.nextIntArray();
        n = tmp[0];
        m = tmp[1];

        ArrayList<Job> j = new ArrayList<>();

        for (int i = 0; i < n; i++) {
            tmp = scanner.nextIntArray();
            int a = tmp[0];
            int b = tmp[1];
            if (a > m)
                continue;
            j.add(new Job(a, b));
        }

        if (j.size() == 0) {
            System.out.println(0);
            System.exit(0);
        }

        Collections.sort(j, new Comparator<Job>() {
            @Override
            public int compare(Job o1, Job o2) {
                if (o1.delay < o2.delay) {
                    return -1;
                } else if (o1.delay > o2.delay) {
                    return 1;
                } else
                    return 0;
            }
        });
        // System.out.println(j);
        PriorityQueue<Job> pq = new PriorityQueue<>(new Comparator<Job>() {
            @Override
            public int compare(Job o1, Job o2) {
                if (o1.reward > o2.reward) {
                    return -1;
                } else if (o1.reward < o2.reward) {
                    return 1;
                } else {
                    if (o1.delay < o2.delay) {
                        return -1;
                    } else if (o1.delay > o2.delay) {
                        return 1;
                    } else
                        return 0;
                }
            }
        });

        // System.out.println(pq.peek());
        long tot = 0;
        int c = 0;
        for (int i = m; i >= 0; i--) {
            while (c < j.size() && m - i == j.get(c).delay) {
                pq.add(j.get(c));
                c++;
            }
            Job el = pq.poll();
            // System.out.println(el);
            if (el != null) {
                tot += el.reward;
            }
        }
        System.out.println(tot);
    }

    public static class Job implements Comparable<Job> {
        int delay, reward;
        public Job(int delay, int reward) {
            this.delay = delay;
            this.reward = reward;
        }
        @Override
        public int compareTo(Job other) {
            if (this.reward < other.reward)
                return -1;
            if (this.reward > other.reward)
                return 1;
            else {
                if (this.delay > other.delay)
                    return -1;
                else if (this.delay < other.delay)
                    return 1;
                else return 0;
            }
        }
        @Override
        public String toString() {
            return this.delay + " " + this.reward;
        }
    }

    private static class FastScanner {
        private BufferedReader br;

        public FastScanner() { br = new BufferedReader(new InputStreamReader(System.in)); }
        public FastScanner(String input) throws Exception { br = new BufferedReader(new FileReader(input)); }
        public int[] nextIntArray() throws IOException {
            String line = br.readLine();
            String[] strings = line.trim().split("\\s+");
            int[] array = new int[strings.length];
            for (int i = 0; i < array.length; i++)
                array[i] = Integer.parseInt(strings[i]);
            return array;
        }
        public int nextInt() throws IOException { return Integer.parseInt(br.readLine()); }
        public long[] nextLongArray() throws IOException {
            String line = br.readLine();
            String[] strings = line.trim().split("\\s+");
            long[] array = new long[strings.length];
            for (int i = 0; i < array.length; i++)
                array[i] = Long.parseLong(strings[i]);
            return array;
        }
        public ArrayList<Integer> nextIntegerArrayList() throws IOException {
            String line = br.readLine();
            String[] strings = line.trim().split("\\s+");
            ArrayList<Integer> array = new ArrayList<Integer>();
            for (int i = 0; i < strings.length; i++)
                array.add(Integer.parseInt(strings[i]));
            return array;
        }
        public ArrayList<Long> nextLongArrayList() throws IOException {
            String line = br.readLine();
            String[] strings = line.trim().split("\\s+");
            ArrayList<Long> array = new ArrayList<Long>();
            for (int i = 0; i < strings.length; i++)
                array.add(Long.parseLong(strings[i]));
            return array;
        }
        public long nextLong() throws IOException { return Long.parseLong(br.readLine()); }
        public double nextDouble() throws IOException { return Double.parseDouble(br.readLine()); }
        public String nextLine() throws IOException { return br.readLine(); }


        public ArrayList<BigInteger> nextBigIntegers() throws IOException {
            String line = br.readLine();
            String[] strings = line.trim().split("\\s+");
            ArrayList<BigInteger> array = new ArrayList<BigInteger>();
            for (int i = 0; i < strings.length; i++)
                array.add(BigInteger.valueOf(Long.valueOf(strings[i])));
            return array;
        }
    }
}