From A to B, a telegraph pole was originally installed every 45 meters, plus the two telegraph poles at both ends, a total of 21. Now it is changed to install a utility pole every 60 meters. Except for the one at the starting end that does not need to be moved, how many poles in the middle do not need to be moved?
从甲地到乙地原来每隔45米安装一根电线杆，加上两端的两根电线杆共21根．现在改成每隔60米安装一根电线杆，除起始端的一根不需移动外，中间还有多少根不必移动？
<gadget id="calculator">21 - 1</gadget>
<output>20</output>

<gadget id="calculator">2 * 2 * 3 * 3 * 5</gadget>
<output>180</output>

<gadget id="calculator">20 / 180</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">45 * (1/9)</gadget>
<output>5</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<result>4</result>