Thank you for clearifying that

Hi- "Assume that the front person in the queue proceeds to a till as soon as it becomes free."

In your case the last person would go to the second till (the first to become free).

I just want to ask that how the queue is created?
I mean are the people distributed evenly across all the tills or they can just hop between till whenever they are empty? eg

if int[5,1,2,1] and there are 3 tills, so the last person goes to the first till and waits for 5 min or he can go to the other till that is occupied, i.e the second index in this case.

Please help me understand this situation