There are only 3 story books and 5 undergraduate teaching books in the bookcase. To ensure that two of the same books are taken out at a time, how many books must be taken out at least?
书橱里只放着3本故事书和5本科教书．要保证一次拿出两本同样的书，至少要拿出多少本书？
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>