#!/usr/bin/env python


__author__ = "Mia Stein"

'''
Cesar Ecrypt
'''

import sys


def encrypt(message, k):
    alphabet = list('abcdefghijklmnopqrstuvwxyz ')
    cipher = ''
    for c in message:
        cipher += alphabet[(alphabet.index(c) + k)%(len(alphabet))]
    return cipher


def decrypt(message, k):
    alphabet = list('abcdefghijklmnopqrstuvwxyz ')
    decipher = ''
    for c in message:
        decipher += alphabet[(alphabet.index(c) - k)%(len(alphabet))]
    return decipher


def main():
    MESSAGE = list(raw_input('Enter the message to be encrypted: ')) or "all your basis belong to us"
    k = 13

    encrypted_msg = encrypt(MESSAGE, k)
    print("Encrypted message: " + encrypted_msg)


    decrypted_msg = decrypt(encrypted_msg, k)
    assert(decrypted_msg == MESSAGE)


if __name__ == '__main__':
    main()