There are three kinds of weights of 2 grams, 3 grams and 4 grams each, which are divided into 17 piles. If you want to take out 1 gram from each pile (weights are allowed to be exchanged between piles, for example, pile A has two 2-gram weights, pile B has one 3-gram weight, and after the exchange, pile A has a 3-gram weight Weights, there is a 2-gram weight in pile B, and one 2-gram weight is taken out, so that 1-gram weights are taken out from the two piles of A and B respectively). So how many weights should these 17 piles have at least?
有2克、3克、4克三种砝码各若干个，分成17堆．如果要在每堆中各取出1克(允许各堆之间交换砝码，例如甲堆有两个2克砝码，乙堆有1个3克砝码，交换后成为甲堆有一个3克砝码，乙堆有一个2克砝码，取出2克砝码一个，这样甲乙两堆中就各取出1克砝码)．那么这17堆至少要有多少个砝码．
<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">21 + 5</gadget>
<output>26</output>

<result>26</result>