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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
//error_reporting(0);
//$N = trim(fgets(STDIN));
list($N,$M) =  explode(" ",trim(fgets(STDIN)));
//$H =  explode(" ",trim(fgets(STDIN)));
for($i=0;$i<$N;$i++) {
  list($A,$B) =  explode(" ",trim(fgets(STDIN)));
  $m[$M-$A][]=$B;
}
$pq = new SplPriorityQueue();
$pq->setExtractFlags(SplPriorityQueue::EXTR_PRIORITY);
$res=0;
for($i=$M;$i>=0;$i--) {
  if (isset($m[$i])) {
    foreach($m[$i] as $v) {
      $pq->insert($v,$v);
    }
  }
  if ($pq->isEmpty()==false) {
    $res += $pq->extract();
  }
}
printf("%d\n",$res);