On the west side of the school, it was originally planned to plant a poplar tree every 5 meters. Adding the two trees at both ends, the total is 25. Now it is changed to plant a poplar tree every 6 meters. Except for the two trees at both ends, there is no need to move. How many trees do not need to be moved in the middle of the original plan?
学校西侧原来计划每隔5米栽一棵杨树，加上两端的两棵一共是25棵，现在要改成每隔6米栽一棵杨树，除两端的两棵不需要移动外，原计划的中间有多少棵不必移动？
<result>3</result>