Xiao Ming planted colorful flags around the playground. At the beginning, he inserted one every 4 meters. After 11, he found that the colorful flags were not enough, so he decided to reinsert them and changed to one every 5 meters. When replugging, how many colored flags do not need to be unplugged and replugged?
小明在操场四周插彩旗，开始时每隔4米插一面，插了11面后，发现彩旗不够，于是决定重插，改为每隔5米插一面．在重插时，有几面彩旗不需要拔掉再插？
<gadget id="calculator">11 - 1</gadget>
<output>10</output>

<gadget id="calculator">10 / 20</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">4 * (1/2)</gadget>
<output>2</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>