If a series of numbers 1, 4, 7, 10, ..., 397, 400 are multiplied together, what is the number of zeros at the end of the resulting product?
一串数1、4、7、10、…、397、400相乘，则所得的积的尾部零的个数为多少．
<gadget id="calculator">400 - 10</gadget>
<output>390</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">390 / 15</gadget>
<output>26</output>

<gadget id="calculator">26 + 1</gadget>
<output>27</output>

<gadget id="calculator">27 + 5 + 2</gadget>
<output>34</output>

<result>34</result>