There are 40 students in class 1 of the sixth year. The teacher needs to call to inform everyone about something urgent. Please help the teacher to design a plan so that the teacher can notify every student in the shortest time. If it takes 1 minute to make a phone call, how long does your design take at least?
六年1班有40名同学，老师有急事要打电话通知大家，请你帮助老师设计一个方案，让老师在最短的时间里通知到每一个同学．如果打一个电话需要1分钟，你设计的方案至少要用多少时间？
<result>6</result>