(1/6), (2/7), (3/8), ... (1987/1992) how many simple fractions.
(1/6)，(2/7)，(3/8)，…(1987/1992)中有多少个最简分数．
<gadget id="calculator">6 / 1</gadget>
<output>6</output>

<gadget id="calculator">1_992 - 6</gadget>
<output>1_986</output>

<gadget id="calculator">1_990 / 5</gadget>
<output>398</output>

<gadget id="calculator">398 - 1</gadget>
<output>397</output>

<gadget id="calculator">1 - 397</gadget>
<output>-396</output>

<gadget id="calculator">1_986 + (-396)</gadget>
<output>1_590</output>

<result>1_590</result>