The teacher asked Xiao Ming to put some flags on the 400-meter circular runway for marking according to the following rules: starting from the starting point, a flag was inserted every 90 meters along the runway until the next 90 meters has been planted with a flag, So how many flags should Xiao Ming prepare?
老师让小明在400米的环形跑道上按照如下规律插上一些旗子做标记：从起点开始，沿着跑道每前进90米就插上一面旗子，直到下一个90米的地方已经插有旗子为止，则小明要准备多少面旗子．
<gadget id="calculator">3_600 / 90</gadget>
<output>40</output>

<result>40</result>