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[] a = new int[n];
      int[] b = new int[n];

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

      int ans = 0;

      int maxbefore = 0;
      int maxb = 0;
      int flag = -1;

for(int i=1;i<=m;i++){ //i=1,2,...,m
//////////////////////////////////////////////////////
for(int j=0;j<n;j++){ //check maximum Bj with Aj<=i
  if(a[j]<=i){
  //////////////////////////////////////////////////
    maxbefore = maxb;
    maxb = Math.max(maxb,b[j]);
    //System.out.println("when i="+i+",when j="+j+",maxb="+maxb+",b["+j+"]="+b[j]);
    if(maxbefore!=maxb){ // if maxb is renewed
      flag = j;
    }
  //////////////////////////////////////////////////
  }
}
ans += maxb;
if(flag!=-1){
  b[flag] = 0; //avoid reselection
}
maxbefore = 0;
maxb = 0;
//System.out.println("when i="+i+",ans="+ans);
//////////////////////////////////////////////////////
}


    System.out.println(ans);

    }
}