using System;
using System.IO;
class MainClass
{
    static void displaymenu()
    {
        Console.WriteLine("Menu");
        Console.WriteLine("1) Encrypt.");
        Console.WriteLine("2) Decrypt.");
        Console.WriteLine("3) Quit.");
    }
    static string Encode(string message, int key)
    {
        int ASCIICode, LetterNumber;
        string NewMessage = "";
        for (int i = 0; i < message.Length; i++)
        {
            if (message[i] >= 'a' && message[i] <= 'z')
            {
                LetterNumber = (int)message[i] - 97;
                LetterNumber = (LetterNumber + key) % 26;
                if (LetterNumber < 0) LetterNumber += 26;
                ASCIICode = LetterNumber + 97;
                NewMessage += Convert.ToChar(ASCIICode);
            }
            else if (message[i] >= 'A' && message[i] <= 'Z')
            {
                LetterNumber = (int)message[i] - 65;
                LetterNumber = (LetterNumber + key) % 26;
                if (LetterNumber < 0) LetterNumber += 26;
                ASCIICode = LetterNumber + 65;
                NewMessage += Convert.ToChar(ASCIICode);
            }
            else
                NewMessage += message[i];
        }
        return NewMessage;
    }
    static void Main(string[] args)
    {
        //do while with file exists
        string message, NewMessage;
        Console.WriteLine("Enter the file name you want to decypt include file extension");
        string file = Console.ReadLine();
        StreamReader ReadingFromFile = new StreamReader(file);
        string[] Text = File.ReadAllLines(file);
        int key = Convert.ToInt32(Text[0]);
        for (int i = 1; i < (Text.Length-1); i++)
        {
            Console.WriteLine(Encode(Text[i], -key));
        }
        Console.ReadLine();
    }
}