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 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;

namespace ABC135
{
    class A
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            string[] input = Console.ReadLine().Split(' ');

            int[] array = new int[N];
            for (int i = 0; i < N; i++)
            {
                array[i] = int.Parse(input[i]);
            }

            if (String.Concat(array.Select(x => x)) == String.Concat(array.OrderBy(a => a)))
            {
                Console.WriteLine("YES");
                return;
            }

            for (int i = 0; i < N; i++)
            {
                for (int j = i + 1; j < N; j++)
                {
                    if (array[j] < array[i])
                    {
                        array = Swap(array, i, j);

                        if (String.Concat(array.Select(x => x)) == String.Concat(array.OrderBy(a => a)))
                        {
                            Console.WriteLine("YES");
                            return;
                        }
                        array = Swap(array, j, i);
                    }
                }
            }

            Console.WriteLine("No");

        }

        static int[] Swap(int[] array, int i, int j)
        {
            int tmp = array[i];
            array[i] = array[j];
            array[j] = tmp;

            return array;
        }


    }
}