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(void){
    int N, i,a,b,c,d,j;
    int p[50], y=0, n=0;

    scanf("%d",&N);
    for( i=0; i<N;i++)
    scanf("%d",&p[i]);

    for(i=0; i<N-1;i++){
         if(p[i]>p[i+1] && b ==0){
            a=p[i];
            b=1;
            j=i;
         }
         if(b == 1 && p [i]>p[i+1]){
             c=p[i];    
             p[i]=a;
             p[j]=c;
             b = 2;
         }

    for(i=0; i < N-1;i++){
        if(p[i]>p[i+1])
            n=1;        
    }
    if (n==1)
        printf("NO\n");

        else
        {
            printf("YES\n");
        }
        

    }

}