calculator designed by Xiao Ming has only one function key, press the first time to subtract 19, press the second time to add 17, press the third time to subtract 19, and the fourth time to add 17,..., now input the first A number is 20, please press the function key continuously, at least after the number of times the calculator displays the number is still O.
小明设计的一台计算器，只有一个功能键，按第一次是减19，按第二次是加17，按第三次是减19，第四次是加17，…，现在先输入第一个数是20，请你连续地按功能键，至少按到第多少次后，计算器显示得数仍为O．
<gadget id="calculator">20 - 19</gadget>
<output>1</output>

<gadget id="calculator">19 - 17</gadget>
<output>2</output>

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

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

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

<result>2</result>