// Write a program to convert from any numeral system of given base s to any other numeral system of base d (2 ≤ s, d ≤  16).



using System;
using System.Collections.Generic;
using System.Numerics;
class ConvertFromAnyToAnyNumSystem
{
    static void Main()
    {
        Console.Write("What numeral system will be your entered number (choose from 2 to 16): ");
        int defaultNumericSystem = int.Parse(Console.ReadLine());
        Console.Write("OK! Now write your number in \"{0}\" numeral system: ", defaultNumericSystem);
        string number = Console.ReadLine();
        Console.Write("Now choose to which numeral system you want to convert it (from 2 to 16) ?: ");
        int wantedSystem = int.Parse(Console.ReadLine());

        string decimalResult = AnyNumeralSystemToDecimal(number, defaultNumericSystem);
        string result = ConvertDecimalToAnyOther(decimalResult, wantedSystem);
        Console.WriteLine("The number {0} in \"{1}\" numeral system is = {2}\n", number, wantedSystem, result);

    }

    static string AnyNumeralSystemToDecimal(string number, int choise)
    {
        int[] numberDigits = new int[number.Length];
        string[] hexDigitsAfterTen = { "A", "B", "C", "D", "E", "F", };

        if (choise <= 9)
        {
            for (int i = 0; i < number.Length; i++)
            {
                numberDigits[i] = (char)(char.GetNumericValue(number[i]));
            }
        }

        else
        {
            for (int i = 0; i < number.Length; i++)
            {
                if (number[i] == 'A' || number[i] == 'a')
                {
                    numberDigits[i] = 10;
                }
                else if (number[i] == 'B' || number[i] == 'b')
                {
                    numberDigits[i] = 11;
                }

                else if (number[i] == 'C' || number[i] == 'c')
                {
                    numberDigits[i] = 12;
                }
                else if (number[i] == 'D' || number[i] == 'd')
                {
                    numberDigits[i] = 13;
                }
                else if (number[i] == 'E' || number[i] == 'e')
                {
                    numberDigits[i] = 14;
                }
                else if (number[i] == 'F' || number[i] == 'f')
                {
                    numberDigits[i] = 15;
                }
                else
                {
                    numberDigits[i] = (char)char.GetNumericValue(number[i]);
                }
            }
        }

        Array.Reverse(numberDigits);
        int holder = 0;
        int result = 0;

        for (int i = 0; i < numberDigits.Length; i++)
        {
            holder = numberDigits[i] * ((int)Math.Pow(choise, i));
            result += holder;
        }
        return result.ToString();
    }

    static string ConvertDecimalToAnyOther(string decimalNumber, int secondChoise)
    {
        BigInteger decimalNumberConverted = BigInteger.Parse(decimalNumber);
        List<string> convertedNumber = new List<string>();
        int remainder = 0;

        if (secondChoise <= 9)
        {
            while (decimalNumberConverted != 0)
            {
                remainder = (int)(decimalNumberConverted % secondChoise);
                decimalNumberConverted = decimalNumberConverted / secondChoise;
                convertedNumber.Add(remainder.ToString());
                if (decimalNumberConverted == 0)
                {
                    break;
                }
            }
            convertedNumber.Reverse();
            string result = "";
            for (int i = 0; i < convertedNumber.Count; i++)
            {
                result += convertedNumber[i];
            }
            return result;
        }

        else
        {
            int[] hexNumbersAfterTen = { 10, 11, 12, 13, 14, 15 };
            List<string> result = new List<string>();
            int holder = 0;

            for (int i = 0; i < decimalNumber.Length; i++)
            {
                holder = (int)(decimalNumberConverted % secondChoise);
                result.Add(holder.ToString());
                decimalNumberConverted /= 16;
                if (holder > 9)
                {
                    if (result[i] == "10")
                    {
                        result[i] = "A";
                    }
                    else if (result[i] == "11")
                    {
                        result[i] = "B";
                    }
                    else if (result[i] == "12")
                    {
                        result[i] = "C";
                    }
                    else if (result[i] == "13")
                    {
                        result[i] = "D";
                    }
                    else if (result[i] == "14")
                    {
                        result[i] = "E";
                    }
                    else if (result[i] == "15")
                    {
                        result[i] = "F";
                    }
                }
            }
            result.Reverse();
            decimalNumber = "";

            for (int i = 0; i < result.Count; i++)
            {
                decimalNumber += result[i];
            }
            return decimalNumber;
        }
    }
}