The museum has light switches in 5 exhibition rooms side by side. He starts from the first exhibition room, walks to the second room, then to the third room..., goes back to the fifth room, goes to the fourth room, and then goes to the third room..., if at the beginning The lights are on in all five exhibition rooms, so how many rooms are still on after he walked through 100 rooms?
博物馆有并列的5间展室的电灯开关．他从第一间展室开始，走到第二间，再走到第三间…，走到第五间后往回走，走到第四间，再走到第三间…，如果开始时五间展室都亮着灯，那么他走过100个房间后，还有几间亮着灯？
<result>5</result>