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, count;
  cin >> n;
  count = 0;
  
  vector<int> p(n);
  vector<int> p_s(n);
  for(int i=0; i<n; i++) {
    cin >> p.at(i);
    p_s.at(i) = p.at(i);
  }
  
  sort(p_s.begin(), p_s.end());
  for (int i=0; i<n; i++) {
  	if (p.at(i)!=p_s.at(i)) {
    	count++;
    }
  }
  
  if (count==2 || count==0) {
  	cout << "YES" << endl;
    return 0;
  }
  
  cout << "NO" << endl;
  return 0;
  
}