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 Python (3.4.3) (judge verdict: Wrong Answer)

N = int(input())
p_list = list(int(pi) for pi in input().split(' '))

num_opposite = 0
indices = []

for i in range(N-1):
  p_1st = p_list[i]
  p_2nd = p_list[i+1]
  
  if p_1st<=p_2nd:
    pass
  else:
    num_opposite+=1
    if num_opposite==1:
      indices.append(i)
    else:
      indices.append(i+1)
      
  
  if num_opposite >=3:
    break 

if num_opposite == 1:
  print('YES')
elif num_opposite == 2:
  small_idx = indices[0]
  large_idx = indices[1]
  
  p_small = p_list[small_idx]
  p_large = p_list[large_idx]
  
  if (p_small==p_list[large_idx-1]+1) and (p_large==p_list[small_idx+1]-1):
    print('YES')
  else:
    print('NO')
else:
  print('NO')