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 main(void)
{
    int n,p[50],i=0,j=0,tmp,k=0,l,m=0;
    scanf("%d",&n);
    for(l=0;l<n;l++)
        scanf("%d",&p[l]);
    while((i==0)&&(k<n)){
        if(k+1!=p[k])
            i=k;
        k++;
    }
    while((j==0)&&(k<n)){
        if(k+1!=p[k])
            j=k;
        k++;
    }
    if((i!=0)||(j!=0)){
    tmp=p[i];
    p[i]=p[j];
    p[j]=tmp;
    }
    for(l=0;l<n;l++)
        if(l+1==p[l])
            m++;
    if(m==n)
        printf("YES\n");
    else
        printf("NO\n");
    return 0;
}