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>
#include<stdlib.h>

int main(void){
  int N,i;
  int* p;
  int count=0;
  scanf("%d",&N);
  int first_num=N,first_val,second_num=N,second_val;
  p=(int*)malloc(sizeof(int)*N);
  for(i=0;i<N;i++){
    scanf("%d",&p[i]);
    if((i+1)!=p[i]){
      count++;
      if(first_num==N){
        first_num=(i+1);
        first_val=p[i];
      }else{
        if(second_num==N){
          second_num=(i+1);
          second_val=p[i];
        }
      }
    }
  }
  if(count==0){
    printf("YES\n");
  }else{  
     if(count==2){
       if((first_num==second_val)&&(first_val==second_num)){
          printf("YES\n");
        }else{
          printf("NO\n");
        }
      }else{
        printf("NO\n");
    }
  }
  return 0;
}