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 a,i,j,c=0,c1=0,r=0,r1=0;
    scanf("%d",&a);
    int b[a];
    for(i=1;i<=a;i++)
    {
        scanf("%d",&b[i]);
    }
    for(i=1,j=a;i<=a;i++,j--)
    {
        if(b[i]==i)
            c++;
        if(b[i]==j)
            c1++;
    }
    if(c==a)
        printf("YES");
    else if(c==a-2)
    {
        for(i=1;i<a;i++)
        {
            if(b[i]!=i)
            {
                b[i]==i;
                r++;
            }
        }
        if(r==2)
            printf("YES");
        else
            printf("NO");
    }
    else if(c>0 && c<a-2)
        printf("NO");
    else if(c1==a)
        printf("YES");
    else if(c1==a-2)
    {
        for(i=1,j=a;i<=a;i++,j--)
        {
            if(b[i]!=j)
            {
                b[i]==j;
                r1++;
            }
        }
        if(r1==2)
            printf("YES");
        else
            printf("NO");
    }
    else if(c1>0 && c1<a-2)
        printf("NO");
}