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: Wrong Answer)

#include <stdio.h>
int main()
{
    int n, arr[50], i, count=0, a[2], j=0;
    scanf("%d", &n);
    for(i=1; i<=n; i++)
    {
        scanf("%d", &arr[i]);
        if(i!=arr[i])
        {
            count++;
            a[j]=i;
            j++;

        }
    }
    if(count==2)
        printf("YES\nYou can sort p in ascending order by swapping p_%d and p_%d.\n", a[0], a[1]);
    else if(count==0)
        printf("YES\np is already sorted in ascending order, so no operation is needed.\n");
    else
        printf("NO\nIn this case, swapping any two elements does not sort p in ascending order.\n");
}