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 Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

(defparameter *k* 1)
(defparameter *l* 0)

(defun cnt (lst)
  (if lst
      (progn (unless (equal (car lst) *k*)
	       (setf *l* (+ *l* 1)))
	     (setf *k* (+ *k* 1))
	     (cnt (cdr lst))
	     )
      *l*
      )
  )
 
      
	  
(let* ((n (read))
       (lst (loop :repeat n :collect (read)))
       )
(if (member (cnt lst) '(0 2))
    (princ "YES")
    (princ "NO")
    )
)