def find_empty_col(slots):
    """Find empty col in slots.

    Args:
        slots (dict): slots for answer

    Returns:
        int: available col for insert
             6 --> no available col
             others --> col index

    """
    index = 0
    for i in list(zip(*list(slots.values())[::])):
        if sum([1 for j in list(i) if j]) == 0:
            return index
        index += 1
    return 6