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>
#include <stdlib.h>
#include <string.h>
#include <memory.h>
#include <math.h>

int main (int argc, char **argv)
{
  int n = 0;
  int p[50] = {0};
  int i = 0;
  int j = 0;
  int op = 0;

  scanf("%d", &n);

  for(i = 0; i < n; i++)
  {
    scanf("%d", &p[i]);
  }

  for(i = 1; i < n; i++)
  {
    if(p[i] < p[i - 1])
    {
      if(op)
      {
        printf("NO\n");
        return 0;
      }
      for(j = i + 1; j < n; j++)
      {
        if(p[i - 1] < p[j])
        {
          int tmp = p[i - 1];
          p[i - 1] = p[j];
          p[j] = tmp;
          op++;
        }
      }
    }
  }

  printf("YES\n");

  return 0;
}