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(){
  int i,j,k;
  int N;
  scanf("%d",&N);
  int A[N+1];
  int flg=0;
  for(i=1;i<=N;i++)
    scanf("%d ",&A[i]);
  int tmp;
  for(i=1;i<=N;i++){
    if(i!=A[i]){
      if(flg==1){
        puts("NO");
        return 0;
      }
      if(A[A[i]] != i){
        puts("NO");
        return 0;
      }
      else{
        tmp=A[A[i]];
        A[A[i]]=A[i];
        A[i] = tmp;
        flg=1;
      }
    }
  }
  puts("YES");
  return 0;
}