There are 6 water glasses as shown in the picture below:
You need to turn all of them upside down with the rules below:
- You have to choose any 5 of them at every turn.
- Chosen ones need to be turned upside down (if they are at the original position) or back to the original position (if they are already upside down).
So, at least, how many turns do you need to turn all 6 of them upside down?