What is the sum of the simplest proper fractions whose denominator is 400?
分母是400的最简真分数的和是多少．
<gadget id="calculator">400 / 5</gadget>
<output>80</output>

<gadget id="calculator">200 - 80</gadget>
<output>120</output>

<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<result>60</result>