import re

def letters_finding(text:str):
    ret=""
    # 将所有字母替换为小写字母
    text=text.lower()
    # 使用正则表达式查找所有字母
    letters = re.findall(r'[a-zA-Z]', text)
    for letter in letters:
        ret+=letter
    return ret

def shift_cipher_encryption(m:str,k:int):
    letters=letters_finding(m)
    cipher=""
    for letter in letters:
        cipher+=chr(((ord(letter) - ord('a') + k) % 26) + ord('a'))
    return cipher

def shift_cipher_decryption(c:str,k:int):
    return shift_cipher_encryption(c,-k)