Statement

With the \circledU button, the elevator goes up one floor; with the \circledD button, it goes down one floor; and the \circled0 button takes the passenger directly to the ground floor. We know which floor is the lowest (\mathttlo), which is the highest (\mathtthi), and the current position of the elevator (\mathttpos). Your task is to determine which floor the elevator will end up on based on the sequence of pressed buttons. If the elevator would move to a non-existent floor, output an error ("error"). (Note: the building may also include underground levels.)