using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var arrangements = new Arrangements("123456789");

        //Console.WriteLine(arrangements.panel_count(3));

        var result = arrangements.panel_shuffles(4);

        Console.WriteLine(result.Count);

        foreach (var item in result)

        {

            Console.WriteLine(item);

        }

    }

}

​

public class Arrangements

{

    private string initialNames;

    public Arrangements() : this(PrepareList())

    {

    }

    public Arrangements(string thenames)

    {

        initialNames = thenames;

    }

    public static string PrepareList()

    {

        var str=string.Empty;

        for (int i = 0; i < 26; i++)

        {

            str += (char)('a' + i);

        }

        for (int i = 0; i < 26; i++)

        {

            str += (char)('A' + i);

        }

        return str;

    }

​

    public List<string> panel_shuffles(int n)

    {

        if(n>initialNames.Length)

            throw new Exception(n.ToString());

        var currentNames = initialNames.Substring(0, n);

        var result = new List<string>();

        if(n==0) return result;

        result.Add(currentNames);

        if(n==1) return result;

        result.AddRange(panel_shuffle(currentNames, 0));

        return result;

    }

​

    public List<string> panel_shuffle(string str, int pos)

    {

        var result = new List<string>();

        var str2 = str.Substring(0,pos);

        str2 += str[pos+1];

        str2 += str[pos];

        if(pos<str.Length-1){

            str2 += str.Substring(pos+2);

        }

        result.Add(str2);

        if(pos < str.Length-2){

            result.AddRange(panel_shuffle(str, pos+1));

        }

        if(pos < str.Length-3){

            result.AddRange(panel_shuffle(str2, pos+2));

        }

        return result;

    }

​

    public double panel_count(int n)

    {

        if(n==0)return 0;

        return fibonacci(0, 1, n);

    }

​

    public int fibonacci(int a, int b, int n)

    {

        if(--n == 0)

            return a+b;

        return fibonacci(b, a + b, n);

    }

}