10, assuming 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.
The first day 10 draws 4, assuming 1, 2, 3, 4,
The next day, the remaining six people draw 4, assuming 5, 6, 7, 8,
On the third day, you must choose the remaining 9 and 10, and then 1-8 to choose two more people.
Then cycle 3 times in 9 days.
If you are unlucky, you can do it four times in six days, and you can not participate in the lucky draw on the ninth day as appropriate.
Hope to adopt ~