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.lang.reflect.Parameter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        final Scanner scanner = new Scanner(System.in);
        final int n = scanner.nextInt();
        final int m = scanner.nextInt();

        final List<Pair> pairs = new ArrayList<>();

        for (int i = 0; i < n; i++) {
            final int days = scanner.nextInt();
            final int value = scanner.nextInt();
            pairs.add(new Pair(days, value));
        }

        pairs.sort((o1, o2) -> o2.getValue() - o1.getValue());

        final boolean[] checked = new boolean[m];

        int res = 0;
        for (final Pair pair : pairs) {
            int days = pair.getDays() - 1;
            if (check(checked, days)) {
                res += pair.getValue();
            }
        }

        System.out.println(res);
    }

    private static boolean check(final boolean[] array, final int index) {
        if (index >= array.length) {
            return false;
        }

        if (!array[index]) {
            array[index] = true;
            return true;
        }

        return check(array, index + 1);
    }

    static class Pair {
        private final int days;
        private final int value;

        public Pair(final int days, final int value) {
            this.days = days;
            this.value = value;
        }

        public int getDays() {
            return days;
        }

        public int getValue() {
            return value;
        }
    }
}