The 1991 students numbered 1 to 1991 from left to right lined up, counted from 1 to 2 from left to right, the students who reported 2 stayed put, and the rest of the students came out; Count from 1 to 2 from left to right, those who reported 2 will stay, and the rest of the students will stand out; the remaining students will count from 1 to 2 from left to right for the third time, the students who reported to 2 will stay, and the rest will go out Columns, such an infinite loop, then what is the initial number of the last student left.
从左向右编号为1至1991号的1991名同学排成一行，从左向右1至2报数，报数为2的同学原地不动，其余同学出列；然后留下的同学再从左向右1至2报数，报数为2的留下，其余同学出列；留下的同学第三次从左向右1至2报数，报到2的同学留下，其余同学出列，这样无限循环，那么最后留下的同学最初编号是多少号．
<gadget id="calculator">2 ** 10</gadget>
<output>1_024</output>

<result>1_024</result>