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 (Clang 3.8.0) (judge verdict: Accepted)

#include <stdio.h>

int main(int argc, char const *argv[]) {
  int N;
  int p[50];
  int counter=0;

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

  for (int i = 0; i < N; i++) {
    if(p[i] != i+1){
      counter++;
    }
  }

  if(counter == 2 || counter == 0){
    printf("YES" );
  }else{
    printf("NO" );
  }
  return 0;

}