$length = count($input);
$result = 'YES';

for ($i=0; $i < $length ; $i++) { 
	if ($input[$i] == $i+1) {
		continue;
	}
	else
	{
			while ($input[$i] !== $i+1) {
				
				$searchElement =  $i+1;
		
				$index = array_search($searchElement, $input);
				
				$diff = $index -$searchElement;

				if($diff == 0)
				{

					 if (!isset($input[$index+1])) {
			          $result = 'NO';
			           break 2; // stop the while loop
			        }

					$first = $input[$index-1]; //5
					$second = $input[$index];//2;
					$third = $input[$index+1];//6

					$input[$index] = $third;
				    $input[$index-1] =$second;
				    $input[$index+1] = $first;

				}
				else
				{

				 $first =$input[$index]; //2
 				 $second =$input[$index-1]; //5
				 $third =$input[$index-2]; //6
				
				$input[$index] = $third;
				$input[$index-1] =$first;
				$input[$index-2] = $second;

				}


			}
			
	}

}
	echo $result;``