def make_product(digits, k, start):
    """
    Compute k numbers product from start position.
    :param digits:
    :param k:
    :param start:
    :return: (product, next_start)
    """
    index = 0
    product = 1
    while index < k and start + index < len(digits):
        if digits[start + index]:
            product *= digits[start + index]
            index += 1
        else:
            # if 0 found, change start to position after 0 and compute product again
            start += index + 1
            index = 0
            product = 1
    if index < k:
        # no k digit product without 0
        return 0, start
    else:
        # return k digit product starting at start position
        return product, start