<?php

// your code goes here

$arr =  array(2,3,4,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12);
$newArr= array();
function find($arr, $current) {
	$i = 0;
	$len = count($arr);
	$mini = $arr[0];
	$minipos = 0;
	for ($i = 0; $i < $len; $i++) {
		if ($arr[$i] < $mini) {
			$mini = $arr[$i];
			$minipos = $i;
		}
		if ($arr[$i] == $current + 1) {
			return $i;
		}
	}
	return $minipos;
}

$current = -1;
while (count($arr)) {
	$pos = find($arr, $current);
	$current = $arr[$pos];
	/*echo $pos.'<br/>';*/
	array_push($newArr, $arr[$pos]);
	array_splice($arr, $pos, 1);
}

echo json_encode($newArr);