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# (Mono-mcs 6.8.0.105) (judge verdict: Accepted)

using System;
using System.IO;

  class Program {
    static void Main(string[] args) {

      int lenA = Convert.ToInt32(Console.ReadLine());
      int[] A = Array.ConvertAll(Console.ReadLine().Split(' '), Temp => Convert.ToInt32(Temp));
      
      for (int i = 0; i < lenA; i++)
      {
        if (A[i] != (i +1))
        {
            int c = A[A[i]-1];
            A[A[i]-1] = A[i];
            A[i] = c;
         break;
        }
        
      }

      for (int i = 0; i < lenA - 1; i++)
      {
          if (A[i]>A[i+1])
          {
            Console.WriteLine("NO");
            return;
          }
        
      }

      Console.WriteLine("YES");
      return;
    }
  }

    // static int[] climbingLeaderboard(int[] scores, int[] alice) {
    //   int[] ans = new int[] { 5, 4, 3, 2, 1 };
    //   return ans;
//int[] alice = Array.ConvertAll(Console.ReadLine().Split(' '), aliceTemp => Convert.ToInt32(aliceTemp));

    // }