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 n;
  int p[50];
  int a[50];
  int i;
  int cnt=0;
  scanf("%d" ,&n);

  for(i=0;i<n;i++){
  	scanf("%d" ,&p[i]);
  }
  for(i=0;i<n;i++){
  	a[i]=i+1;
  }
  
  for(i=0;i<n;i++){
  
    if(p[i]==a[i]) cnt++;
    
  }
  
  
  if((cnt==n-2)||(cnt==n)){
  printf("YES");
  }
  else{
    printf("NO");
  }
  
  return 0;
}