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 = intval(fgets(STDIN));
  $array = explode(" ", trim(fgets(STDIN)));

  $idx1 = -1;
  for($i=0; $i<$n; $i++){
    if($idx1==-1 && $i<$n-1){
      if($array[$i] > $array[$i+1]){
        $idx1 = $i;
      }
    }else if($idx1!=-1){
      if($array[$i] < $array[$idx1+1]){
        $tmp = $array[$i];
        $array[$i] = $array[$idx1];
        $array[$idx1] = $tmp;
        break;
      }
    }
  }

  $result = true;
  for($i=0; $i<$n-1; $i++){
    if($array[$i] > $array[$i+1]){
      $result = false;
      break;
    }
  }

  if($result){
    echo "YES\n";
  }else{
    echo "NO\n";
  }