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>

// useage : swap(&int1,&int2);
// 値入れ替え
int swap(int *c1,int *c2){
  int tmp;
  tmp=*c1;
  *c1=*c2;
  *c2=tmp;
  return 0;
}

int main(void) {
 
  // 入力
  int n;
  scanf("%d",&n);
  int list[n];
  for(int i=0;i<n;i++){
    scanf("%d",&list[i]);
  }
  
  for(int i=1;i<n;i++){
      if(list[i-1]>list[i]){
        int j = i-1;
        while(i<n-1){
          if(list[i]>list[i+1]){
            swap(&list[i+1],&list[j]);
            break;
          }
          i+=1;
        }
        break;
      }
  }
  
  int flg=1;
  for(int i=1;i<n;i++){
    if(list[i-1]>list[i]){
      flg=0;
      break;
    }
  }
  
  if(flg==1)printf("YES\n");
  else      printf("NO\n");

  return 0;
}