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
$n=trim(fgets(STDIN));
$p=explode(" ",trim(fgets(STDIN)));
$s=0;
$i=0;
while($i<$n){
  if($p[$i]!=$i+1){
    if($s==0){
      if($p[$p[$i]-1]==$i+1){
        ++$s;
        $p[$p[$i]-1]=$p[$i];
      }else{
        echo "NO";
        exit;
      }
    }else{
      echo "NO";
      exit;
    }
  }
  ++$i;
}
echo "YES";