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())

A = list(map(int, input().split()))

dis = True
count = 0
for i in range(0, N-1):
    if A[i] > A[i+1]:
        count += 1
        dis = False
        if count == 1:
            tmp1 = i
        elif count == 2:
            tmp2 = i+1

if dis == False and count > 1:
    tmp = A[tmp1]
    A[tmp1] = A[tmp2]
    A[tmp2] = tmp

    count = 0
    for i in range(0, N-1):
        if A[i] > A[i + 1]:
            count += 1
            dis = False
            if count == 1:
                tmp1 = i
            elif count == 2:
                tmp2 = i + 1
    if count == 0:
        dis = True

if dis == True:
    print('YES')
else:
    print('NO')