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.util.*;

public class Main{
    public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);

      int n = sc.nextInt();
      int m = sc.nextInt();

      int[][] x = new int[n][2];

      for(int i=0;i<n;i++){
        x[i][0] = sc.nextInt();
        x[i][1] = sc.nextInt();
      }

      int ans = 0;
      int cnt = -1;
      int max = 0;

      Arrays.sort(x, (a, b)->a[0]-b[0]);

      for(int i=1;i<=m;i++){
        for(int j=0;j<n;j++){
          if(x[j][0]<=i && x[j][1]>max){
            max = x[j][1];
            cnt = j;
          }
        }
        ans += max;
        if(cnt!=-1){
          x[cnt][1] = 0;
        }
        max = 0;
      }

      System.out.println(ans);

    }
}