Description

You will be deciphering a given message. It is encrypted with a Caesar Cipher (https://en.wikipedia.org/wiki/Caesar_cipher) that increases by 2 after every 3 characters (including symbol characters, which are not encoded), starting at key = 5. You should save this message to a file using a text editor. Then, your program will prompt the user for the name of the file, decrypt the message stored in the file, and then write the decrypted message to a new file called solution.txt.
A sample message talking about getting 5 points of extra credit appears below:

HINTS:
• Make sure your key does not exceed 26, the number of letters in the alphabet. Consider using modulo division to help.
• Make sure you “roll” around the alphabet correctly. For example, if the input letter is “D” and the key is currently 5, subtracting 5 from D’s code would result in you being 1 before A (64). You should add back the code for the letter Z to roll to the end of the alphabet.
• For JavaScript/TypeScript coders: You can convert letters to their numerical equivalent numbers by using String.fromCharCode(…) and String.charCodeAt(…). For example, String.fromCharCode(65) produces ‘A’ and ‘A’.charCodeAt(0) produces 65.
• For coders in other languages: You can do math directly with letters, such as ‘D’ – ‘A’.