There are many fish in a fish tank, and there are 4 species in total. How many fish should be caught at least once to ensure that there are 5 fish of the same species.
一只鱼缸里有很多条鱼，共有4个品种．一次至少捞出多少条鱼，才能保证有5条相同品种的鱼．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">16 + 1</gadget>
<output>17</output>

<result>17</result>