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: Wrong Answer)

<?php
fscanf(STDIN, "%d %d", $n, $m);
while ($n--) {
	fscanf(STDIN, "%d %d", $a, $b);
	$q[] = [$a, $b];
}
usort($q, 'cmp');
$x = 0;
foreach ($q as $v) {
	if ($v[0] <= $m) {
		$x += $v[1];
		if (--$m == 0) break;
	}
}
echo $x;

function cmp($a, $b) {
	if ($a[1] > $b[1]) {
		return -1;
	} elseif ($a[1] < $b[1]) {
		return 1;
	} else {
		if ($a[0] == $b[0]) return 0;
		return ($a[0] > $b[0]) ? -1 : 1;
	}
}