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;
using System.Collections.Generic;

class Program
{
    public static void Main()
    {


        var N = int.Parse(Console.ReadLine());
        var line = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();

        List<int> list = new List<int>();

        bool a = true;

        for(int i = 0;i < N;i++ )
        {


            if (i != N - 1 && a)
            {
                if (line[i + 1] < line[i]) //昇順じゃない
                {
                    list.Add(i);
                    a = false;
                }
            }
            else if (i != N - 1 && !a)
            {
                if (line[i + 1] < line[i]) //昇順じゃない
                {
                    list.Add(i + 1);
                }
            }


        }


        if (list.Count() == 0)
        {
            Console.WriteLine("YES");
        }
        if(list.Count() == 2)
        {
            int u = line[list[0]];
            line[list[0]] = line[list[1]];
            line[list[1]] = u;

            for (int i = 0; i < N; i++)
            {
                if (i != N - 1)
                {
                    if (line[i + 1] < line[i]) //昇順じゃない
                    {
                        Console.WriteLine("NO");
                        goto END;
                    }
                }
            }
            Console.WriteLine("YES");
        }
        else
        {
            Console.WriteLine("NO");
        }

    END:;
    }
}