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 PHP (5.6.30) (judge verdict: Time Limit Exceeded)

<?php
fscanf(STDIN, "%d %d", $n, $m);
$a = array();
 
for($i = 0; $i < $n; $i++){
	fscanf(STDIN, "%d %d", $j, $k);
  	if($j > $m){
    	continue;
    }
  	$a[$k][] = $j;
}
krsort($a);
foreach($a as $key =>$value){
	rsort($a[$key]);
}
$cnt = 0;
for($day = $m - 1; $day >= 0; $day--){
  foreach($a as $key => $val){
    foreach($val as $k => $v){
      if($v > $m - $day){
        continue;
      }else{
        $cnt += $key;
        $a[$key][$k] = $m + 1;
        break 2;
      }
  	}
  }
}
echo $cnt;
?>