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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;
int main()
{
  	int n,f=-1,m=-1,s=-1;
  	cin>>n;
  	vector<int> nums(n);
  	for(int i=0;i<n;i++)
    {
      cin>>nums[i];
      if(i>0)
        if(nums[i]<nums[i-1])
        {
          if(f==-1)
          {
            f=i-1;
            m=i;
          }
          else if(s==-1)
          {
            s=i;
          }
        }
    }
	if(f==-1)
    {
      	cout<<"YES\n";
      	return 0;
    }
    if(s==-1)
    {
     	swap(nums[f],nums[m]);
    }
     else
       swap(nums[f],nums[s]);
  	for(int i=0;i<n-1;i++)
    {
     	if(nums[i]>nums[i+1])
        {
          cout<<"NO\n";
          return 0;
        }
    }
      cout<<"YES\n";
	return 0;  
}