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>
#include<math.h>

void swap(int a, int b)
{
  int temp;
  temp = a;
  a = b;
  b = temp;
}

int main()
{
  int i, j, k, N;
  int p[60];
  int temp, count = 0;

  scanf("%d", &N);
  for(i=0; i<N; i++){
    scanf("%d", &p[i]);
  }
  
  for(i=0; i<N; i++){
    for(j=0; j<N; j++){
      temp = p[i];
      p[i] = p[j];
      p[j] = temp;
      //printf("%d\n", p[i]);
      //printf("%d\n", p[j]);
      for(k=0; k<N-1; k++){
         //printf("%d", count); 
        if(p[k+1]-p[k]>0){
          count++;
          //printf("%d", count);  
          if(count == N-1){
            printf("YES");
            return 0;
          }
        }
      }
      temp = p[i];
      p[i] = p[j];
      p[j] = temp;
      count = 0;
    }
  }

  printf("NO");

  return 0;

}