Problem:
Score : 200 points

Problem Statement

We have a sequence p = {p_1,\ p_2,\ ...,\ p_N} which is a permutation of {1,\ 2,\ ...,\ N}.

You can perform the following operation at most once: choose integers i and j (1 \leq i < j \leq N), and swap p_i and p_j. Note that you can also choose not to perform it.

Print YES if you can sort p in ascending order in this way, and NO otherwise.

Constraints

All values in input are integers.

2 \leq N \leq 50

p is a permutation of {1,\ 2,\ ...,\ N}.

Input

Input is given from Standard Input in the following format:

N
p_1 p_2 ... p_N

Output

Print YES if you can sort p in ascending order in the way stated in the problem statement, and NO otherwise.

Sample Input 1

5
5 2 3 4 1

Sample Output 1

YES

You can sort p in ascending order by swapping p_1 and p_5.

Sample Input 2

5
2 4 3 5 1

Sample Output 2

NO

In this case, swapping any two elements does not sort p in ascending order.

Sample Input 3

7
1 2 3 4 5 6 7

Sample Output 3

YES

p is already sorted in ascending order, so no operation is needed.

Solution in PHP7 (7.0.15) (judge verdict: Accepted)

<?php
fscanf(STDIN,"%d",$n);
$m_arr=explode(' ',trim(fgets(STDIN)));
$s_arr=array();
for($i=0;$i<$n;$i++){
	$s_arr[]=$i+1;
}

$chigau_arr=array();
for($t=0;$t<$n;$t++){
	if($m_arr[$t]<>$s_arr[$t]){
		$chigau_arr[]=$t;
	}
}

if(count($chigau_arr)==0){
	echo "YES";
}elseif(count($chigau_arr)==1){
	echo "NO";
}elseif(count($chigau_arr)<>2){
	echo "NO";
}else{
	echo "YES";
}
?>