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: Accepted)

N = int(input())
P = list(map(int,input().split()))

flag = []
for i in range(N-1):
  if P[i] > P[i+1]:
    flag.append(i)

if len(flag) > 2:
  print('NO')
if len(flag) == 2:
  A = P[flag[0]]
  B = P[flag[1]+1]
  P[flag[0]] = B
  P[flag[1]+1] = A
  for i in range(N-1):
    if P[i] > P[i+1]:
      print('NO')
      exit()
  print('YES')
  exit()
if len(flag) == 1:
  A = P[flag[0]]
  B = P[flag[0]+1]
  P[flag[0]] = B
  P[flag[0]+1] = A
  for i in range(N-1):
    if P[i] > P[i+1]:
      print('NO')
      exit()
  print('YES')
  exit()
if len(flag) == 0:
  print('YES')