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)

import copy

def swap(array, i,j,tar1,tar2):
  tmp = tar1 
  array[i] = tar2
  array[j] = tmp
#  print(array)
  return array

def orderd(array):
  orderd_array = sorted(array)
#  print(array,orderd_array)
  for i in range(len(array)):
    if not orderd_array[i]==array[i]:
      return False
  return True

N = int(input())
P = list(map(int,input().split()))
# print(P)
ans = "NO"
flg = False
for i in range(N):
  for j in range(i,N):
    Pi = copy.copy(P)
    Pi = swap(Pi,i,j,Pi[i],Pi[j])
    if orderd(Pi):
      ans = "YES"
      flg=True
      break
  if flg:
    break
#print(P)
print(ans)