In a cube with side length 4, put small balls with diameter 1, how many balls can be put at most.
在一个棱长为4的立方体内，放入直径为1的小球，最多可以放入多少个．
<gadget id="calculator">16 + 9 + 16 + 9 + 16</gadget>
<output>66</output>

<result>66</result>