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 count = 0;

void quick_sort(int a[],int first,int last){

  int temp,k;
  int flag=1;
  int p=a[first];
  int i=first;
  int j=last;

  while(flag){
    while(a[i]<p)
      i++;
    
    while(p<a[j])
      j--;
    
    if(i<j){
      temp=a[i];  a[i]=a[j];  a[j]=temp;
      count++;
      i++;  j--;
    }
    else
      flag=0;
  }

  if(count ==2)
    return ;

  if(first<i-1)
    quick_sort(a,first,i-1);
  
  if(j+1<last)
    quick_sort(a,j+1,last);
  
}


int main(void){
  int N, i;
  scanf("%d", &N);
  int p[N];
  for(i=0; i<N; i++)
    scanf("%d", &p[i]);

  quick_sort(p, 0, N);

  if(count == 1 || count == 0)
    printf("YES\n");
  else if(count > 1)
    printf("NO\n");


  return 0;
}