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)

from sys import stdin


def swqp(ps, li, ri):
    result = ps[:]
    tmp = result[li]
    result[li] = result[ri]
    result[ri] = tmp
    return result


def check(ps):
    for i in range(len(ps) - 1):
        if ps[i] > ps[i + 1]:
            return False
    return True


def main():
    N = int(stdin.readline().rstrip())
    ps = [int(x) for x in stdin.readline().rstrip().split()]
    if check(ps):
        print('YES')
        return
    for i in range(N - 1):
        for j in range(i + 1, N):
            if check(swqp(ps, i, j)):
                print('YES')
                return
    print('NO')


if __name__ == "__main__":
    main()