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: Wrong Answer)

import java.util.*;

public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        ArrayList<Pair> list = new ArrayList<>();
        for(int i = 0; i < n; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            list.add(new Pair(a, b));
        }
        list.sort((x, y) -> {
            if (x.b == y.b) {
                return y.a - x.a;
            } else {
                return y.b - x.b;
            }
        });
        long count = 0;
        for(Pair p: list) {
            int getDays = p.a;
            int payment = p.b;
            if (getDays <= m) {
                count += payment;
                m--;
            }
        }
        System.out.println(count);
    }

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