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()))
foundpair=False
foundi=False
sortedp=sorted(p)
pair=[]
if p==sortedp:
  print("YES")
  exit(0)
for i in range(N):
  if p[i]== sortedp[i]:
    continue
  else:
    if foundpair==False:
      if foundi:
        foundpair=True
        pair.append(i)
      else:
        foundi=True
        pair.append(i)
    else:
      print("NO")
      exit(0)
      
p[pair[0]],p[pair[1]]=p[pair[1]],p[pair[0]]
if p==sortedp:
  print("YES")
else:
  print("NO")