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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php 
  fscanf(STDIN, "%d", $n);
  fscanf(STDIN, "%s", $str);
  $arr = str_split($str);

  $flg = true;
  $tmp = [];
  for($i = 1; $i <= $n; $i++) {
    if($i != $arr[$i-1]) {
      $tmp[] = $i-1;
      $flg = false;
    }
  }
  if($flg) echo "YES";
  if(count($tmp) === 2) {
    echo "YES";
  } else {
    echo "NO";
  }