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
  /*
$x = explode(" ",trim(fgets(STDIN)));
sort($x);

for ($i=0;$i<$x[1];$i++){
if(abs($x[0]-$i)==abs($x[1]-$i)){
echo $i;
exit;
}
}
echo 'IMPOSSIBLE';
*/
$N =trim(fgets(STDIN));
$p = explode(" ",trim(fgets(STDIN)));
$c=0;
for($i=0;$i<$N;++$i){
if($p[$i]!=$i+1){
++$c;
}
}

if($c<=2){
echo 'YES';
}else{
echo 'NO';
}