import hashlib


def get_checksum(address_bytes: bytes) -> bytes:
    """ Calculate double sha256 of address and gets first 4 bytes

        :param address_bytes: address before checksum
        :param address_bytes: bytes

        :return: checksum of the address
        :rtype: bytes
    """
    return hashlib.sha256(hashlib.sha256(address_bytes).digest()).digest()[:4]