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
class Swap0or1  {
    var $N, $p, $cnt;
    
    function __construct() {
        list($this->N) = explode(" ", trim(fgets(STDIN)));
        $this->p = array_map("intval", explode(" ", trim(fgets(STDIN))));
        $this->cnt = 0;
    }
    function __invoke() {
        foreach ($this->p as $key => $val) {
            if ($key + 1 !== $val) {
                $this->cnt++;
            }
        }
        return ($this->cnt === 0 || $this->cnt === 2) ? "YES" : "NO";
    }
}

$Swap0or1 = new Swap0or1();
echo $Swap0or1();