using System;

public class Program

{

    public static void Main()

    { 

        int userInput = 0;

        do 

        {

            Console.Write("Please enter a non-negative integer to encrypt: ");

            userInput = Convert.ToInt32(Console.ReadLine());

        }

        while (userInput <= 0);

        int encryptedInteger = Encrypt(userInput);

        Console.WriteLine("Encrypted Integer: {0:D4}", encryptedInteger);

​

        do

        {

            Console.Write("Please enter a non-negative integer to decrypt: ");

            userInput = Convert.ToInt32(Console.ReadLine());

        }

        while (userInput <= 0);

        int finalDecryptedInteger = Decrypt(userInput);     

        Console.WriteLine("Decrypted Integer: {0:D4}", finalDecryptedInteger);  

    }

    // Method that encrypts an integer.

    public static int Encrypt(int userInput)

    {

        int firstDigit = (userInput / 1000 + 7) % 10;

        int secondDigit = (userInput / 100 + 7) % 10;

        int thirdDigit = (userInput / 10 + 7) % 10;

        int fourthDigit = (userInput / 1 + 7) % 10;

        int newFirstDigit = thirdDigit;

        int newSecondDigit = fourthDigit;

        int newThirdDigit = firstDigit;

        int newFourthDigit = secondDigit;

        int encryptedInteger = newFirstDigit * 1000 + newSecondDigit * 100 +

                               newThirdDigit * 10 + newFourthDigit * 1;

        return encryptedInteger;

    }

    // Method that decrypts an encrypted integer.

    public static int Decrypt(int encryptedInput)

    {

        int decryptedFirstDigit = (encryptedInput / 1000) % 10;

        int decryptedSecondDigit = (encryptedInput / 100) % 10;

        int decryptedThirdDigit = (encryptedInput / 10) % 10;

        int decryptedFourthDigit = (encryptedInput / 1) % 10;

        int newDecryptedFirstDigit = decryptedThirdDigit;

        int newDecryptedSecondDigit = decryptedFourthDigit;

        int newDecryptedThirdDigit = decryptedFirstDigit;

        int newDecryptedFourthDigit = decryptedSecondDigit;

        int decryptedUserInput = newDecryptedFirstDigit * 1000 + newDecryptedSecondDigit * 100 +

                                 newDecryptedThirdDigit * 10 + newDecryptedFourthDigit * 1;

        int finalDecryptedFirstDigit = (decryptedUserInput / 1000 - 7) % 10;

        int finalDecryptedSecondDigit = (decryptedUserInput / 100 - 7) % 10;

        int finalDecryptedThirdDigit = (decryptedUserInput / 10 - 7) % 10;

        int finalDecryptedFourthDigit = (decryptedUserInput / 1 - 7) % 10;

        int finalDecryptedInteger = finalDecryptedFirstDigit * 1000 + finalDecryptedSecondDigit * 100 +

                                    finalDecryptedThirdDigit * 10 + finalDecryptedFourthDigit * 1;

        return finalDecryptedInteger;

    }

}