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 (Clang 10.0.0) (judge verdict: Accepted)

#include<stdio.h>
#define size 100
int main( )
{
    int n , i , num[size] , j , temp , a[size];
    scanf("%d" , &n);
    
    for( i = 1 ; i <= n ; i++)
    {
         scanf("%d" , &num[i]);
         a[i] = num[i] ;
    }
       
    
    for( i = 1 ; i <= n ; i++)
    {
        for( j = 1 ; j < n ; j++)
        {
            if( num[j] > num[j+1])
            {
                 temp = num[j] ;
                 num[j] = num[j+1] ;
                 num[j+1] = temp ;
            }
        }
    }
    
    int count = 0 ;
    for( i = 1 ; i <= n ; i++)
    {
        if( a[i] != num[i] )
            count++ ;
    }
    
    if( count == 0 || count == 2)
        printf("YES\n");
    else 
        printf("NO\n");
    
    return 0;
}