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: Wrong Answer)

<?php
fscanf(STDIN,"%d %d", $n,$m);
for($i=0; $i<$n; $i++){
    $arr[] = explode(" ",trim(fgets(STDIN)));
}

foreach( $arr as $key => $row ) {
  $array_0[$key] = $row["0"];
  $array_1[$key] = $row["1"];
}

array_multisort($array_1,SORT_DESC, SORT_NUMERIC,$array_0,SORT_DESC, SORT_NUMERIC,$arr);


$count = 0;
$s=0;
foreach ($arr as $key => $value){
    if(($arr[$key][0]+$s) <= $m && $s<=$n){
        $count += $arr[$key][1];
    }
    $s++;
}
echo $count;

?>