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 C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>

int main()
{
    int N, a=0, b=0, i, bucket;
    scanf("%d", &N);
    int arr[N], arr2[N];

    for(i=0; i<N; i++)
    {
        scanf("%d", &arr[i]);
    }
    for(i=0; i<N-1; i++)
    {
        if(arr[i+1]<arr[i])
        {
            if(a==0)arr2[a] = i;
            else arr2[a] = i+1;
            a++;
        }
    }
    if(a==0)printf("YES");
    else if(a==2)
    {
        bucket = arr[arr2[0]];
        arr[arr2[0]] = arr[arr2[1]];
        arr[arr2[1]] = bucket;

        for(i=0; i<N-1; i++)
        {
            if(arr[i+1]<arr[i])
            {
                b++;
                break;
            }
        }
        if(b==0)printf("YES");
        else printf("NO");
    }
    else printf("NO");

    return 0;
}