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(){
 int n;
 scanf("%d",&n);
 int p[n];
 for(int a=0;a<n;a++){
     scanf("%d",&p[a]);
 }
 int count=0;
 for(int b=0;b<n-1;b++){
     for(int c=1;c<n-c;c++){
         if(count==0){
             if(p[b]>p[b+c]){int tmp;
                 for(int d=1;d<n-b-c;d++){
                     if(p[b+c]>p[b+c+d]){tmp=b+c+d;}}
                     int tmp2;
                     tmp2=p[b];
                     p[b]=p[tmp];
                     p[tmp]=tmp2;
                     count++;}
             else{}
         }
         else{if(p[b]<=p[b+c]){}
              else{printf("NO\n");return 0;}}
     }
 }
 printf("YES\n");
 return 0;
}