def encode(plain_text: str) -> str:
    encoded_text: str = ""
    weight: int = 0
    for char in plain_text.lower():
        if char.isalpha():
            encoded_text += chr(97 + 25 - (ord(char) - 97))
            weight += 1
        elif char.isdigit():
            encoded_text += char
            weight += 1
        else:
            continue
        if (weight % 5) == 0:
            encoded_text += " "
    # remove space at the end when it exists
    if encoded_text[-1] == " ":
        return encoded_text[0:-1]
    return encoded_text


def decode(ciphered_text: str) -> str:
    decoded_text: str = ""
    for char in ciphered_text.lower():
        if char.isalpha():
            decoded_text += chr(122 - 25 + (122 - ord(char)))
        elif char.isdigit():
            decoded_text += char
        else:
            continue
    return decoded_text