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 a;
  scanf("%d",&a);
  int x[a];
  int i;
  i = 0;
  while (i < a)
  {
    scanf("%d",&x[i]);
    i++;
  }
  i = 0;
  int t;
  t = a;
  int b;
  while (i < a)
  {
    if (t != a && i + 1 != x[i])
    {
      //printf("a%d%d\n",t,i+1);
      b = x[t];
      x[t] = x[i];
      x[i] = b;
      break;
    }
    if (i + 1 != x[i] && t == a)
    {
      //printf("t%d",i);
      t = i;
    }
    i++;
  }
  i = 0;
  while (i + 1 < a)
  {
    //printf("%d%d\n",x[i],x[i + 1]);
    if (x[i] > x[i + 1])
    {
      printf("NO");
      return(0);
    }
    i++;
  }
  printf("YES");
}