Assuming the bank has 2 service windows, n customers will arrive one after another and queue up for service one meter away.
Assuming that the time required by the bank to serve each customer (within the range of [1100]) is known. Whenever a window is available, the next customer walks to that window (this time interval is ignored) and the bank staff serves that customer. Ask the bank how long it will take to serve these customers in total.
5 1 3 3 5 7
0
11