def encrypt_text(cleartext: str = 'Bitcoin', incrementation: int = 13):
    encrypted_text = ''

    for char in cleartext:
        encrypted_text += increment_char(char, incrementation)

    return encrypted_text


def increment_char(char, incrementation: int = 1):
    # converting character to byte
    char_in_bytes = bytes(char, 'utf-8')[0]
    if char_in_bytes + incrementation >= 91 and char_in_bytes < 91 \
            or char_in_bytes + incrementation >= 123:  # z -> 122 | 90 -> Z so go backwards
        new_char_in_bytes = bytes([char_in_bytes - (26 - incrementation)])
    else:
        new_char_in_bytes = bytes([char_in_bytes + incrementation])

    return str(new_char_in_bytes)[2]


def decrypt_text(encrypted_text: str = 'Ovgpbva', incrementation: int = 13):
    cleartext = ''

    for char in encrypted_text:
        cleartext += increment_char(char, 26 - incrementation)

    return cleartext


if __name__ == '__main__':
    print(encrypt_text())
    print(decrypt_text())