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 PyPy3 (2.4.0) (judge verdict: Accepted)

n=int(input())
p=list(map(int,input().split()))
flag=True
for k in range(n-1):
    if p[k+1]<p[k]:
        flag=False
if flag:
    print("YES")
    exit()

for i in range(n-1):
    for j in range(i+1,n):
            a=p[i]
            p[i]=p[j]
            p[j]=a
            flag=True
            for k in range(n-1):
                if p[k+1]<p[k]:
                    flag=False
            if flag:
                print("YES")
                exit()
            else:
                a=p[i]
                p[i]=p[j]
                p[j]=a
print("NO")