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 isAsc(int arr[],int sz,int x,int y,int vX,int vY);


int main()
{
    int input[100],input2[100];
    int CASE,C,i,j;
    scanf("%d",&CASE);

    for(C=0; C<CASE; C++)
    {
        scanf("%d",&input[C]);
    }

    int isPossible=0;
    for(i=0; i<CASE; i++)
    {
        for(j=0; j<CASE; j++)
        {
            for(int k=0; k<CASE; k++)
            {
                //printf("%d ",input[k]);
                input2[k]=input[k];
            }
            //printf("\n");
            //printf("%d %d %d %d\n",i,j, input2[i], input2[j]);
            isPossible = isAsc(input2,CASE,i,j,input2[i],input2[j]);
            if(isPossible==1)
            {
                break;
            }
        }
        if(isPossible==1)
        {
            break;
        }
    }

    if(isPossible==0)
    {
        printf("NO\n");
    }
    else
    {
        printf("YES\n");
    }

    return 0;
}

int isAsc(int arr[],int sz,int x,int y,int vX,int vY)
{
    int i;

    arr[x]=vY;
    arr[y]=vX;

    /*
    for(i=0; i<sz; i++)
    {
        printf("%d ",arr[i]);
    }
    printf("\n");
    */

    for(i=0; i<sz-1; i++)
    {
        if(arr[i]>arr[i+1])
        {
            //printf("0\n\n");
            return 0;
        }
    }
    //printf("1\n\n");
    return 1;
}