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.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        int n = Integer.parseInt(sc.next());
        int m = Integer.parseInt(sc.next());
        Sort[] s = new Sort[n];
        for(int i = 0; i < n; i++){
            s[i] = new Sort(Integer.parseInt(sc.next()), Integer.parseInt(sc.next()));
        }
        Arrays.sort(s);
        
        int ans = 0;
        for(int i = 0; i < m; i++){
            if(i == n){
                break;
            }
            if(s[i].a > (m-i)){
                continue;
            }
            ans += s[i].b;
        }
        
        System.out.println(ans);
    }
}

class Sort implements Comparable<Sort>{
    int a;
    int b;
    
    Sort(int a, int b){
        this.a = a;
        this.b = b;
    }

    @Override
    public int compareTo(Sort s) {
        
        if(this.b > s.b){
            return -1;
        }else if(this.b < s.b){
            return 1;
        }else{
            if(this.a > s.a){
                return -1;
            }else if(this.a < s.a){
                return 1;
            }else{
                return 0;
            }
        }
    }
}