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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program abc135b
   implicit none
   integer :: n, counter, i, j
   integer, allocatable :: p(:), q(:)

   read(*,*) n
   allocate(p(n), q(n))
   read(*,*) p(:)

   do i = 1, n
      q(i) = i
   end do

   counter = 0
   do i = 1, n
      if (p(i) /= q(i)) counter = counter + 1
   end do

   if ( counter <= 2) then
      write(*, *) 'YES'
   else
      write(*,*) 'NO'
   end if
end program abc135b