After adding a certain number to the numerator and denominator of the (1993/1996) fraction, the new fraction obtained is (1997/1998), what is the added number?
(1993/1996)分数的分子、分母同时加上某数后，所得的新分数是(1997/1998)，则加上的这个数是多少．
<gadget id="calculator">5_991 - 1_993</gadget>
<output>3_998</output>

<result>3_998</result>