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;
  int ok=0;
  cin >>N;
  vector<int> p(N);
  int count=0;
  for(int i=0; i<N; i++)
    cin >> p.at(i);
  vector<int> test(N);
  for(int i=0; i<N; i++)
    test.at(i)=p.at(i);
  sort(test.begin(), test.end());
  for(int i=0; i<N; i++){
    for(int j=0; j<N; j++){
      if(i<j){
        swap(p.at(i),p.at(j));
      }
      for(int i=0; i<N; i++){
        if(p.at(i)==test.at(i)){
          count++;
        }
      }
      if(count==N){
        ok++;
      }
      if(i<j){
        swap(p.at(i),p.at(j));
      }
      count=0;
    }
  }
  if(ok==0)
    cout << "NO" << endl;
  else
    cout << "YES" << endl;
}