A classmate first placed a pot of flowers every 8 decimeters around the circular flower bed in front of the auditorium, exactly 15 pots were placed, and now they put a pot of flowers every 5 decimeters, how many pots of flowers do not need to be moved?
某班同学先在礼堂前的圆形花坛的周围每隔8分米放一盆花，正好放了15盆，现改为每隔5分米放一盆花，其中有多少盆花不用移动？
<result>3</result>