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,p[100],a[100];
    int i,h,sorted;
    scanf("%d",&n);
    for(i=0;i<n;i++){
        scanf("%d",&p[i]);
        a[i]=p[i];
    }
    h=n;
    while(h){
        if(h) h=h/1.3;
        sorted=0;
        for(i=0;i<n-h;i++){
            if(p[i]>p[i+h]){
                int tmp=p[i];
                p[i]=p[i+h];
                p[i+h]=tmp;
                sorted=1;
            }
        }
    }
    int cnt=0;
    for(i=0;i<n;i++){
        if(a[i]!=p[i]) cnt++;
        //printf("%d %d\n",a[i],p[i]);
    }
    //printf("%d\n",cnt);
    if(cnt<=2){
        
        puts("YES");
    }else{
        puts("NO");
    }
    return 0;
}