A rectangular parallelepiped carton with a square bottom, unfolding its sides, is exactly a square with a side length of 28 decimeters. How many square decimeters of cardboard are needed to make two such cartons?
一个底面是正方形的长方体纸盒，将它的侧面展开，正好是一个边长为28分米的正方形，做两个这样的纸盒至少需要多少平方分米的纸板？
<gadget id="calculator">28 / 4</gadget>
<output>7</output>

<gadget id="calculator">7 * 7 * 2</gadget>
<output>98</output>

<gadget id="calculator">28 * 7 * 4</gadget>
<output>784</output>

<gadget id="calculator">98 + 784</gadget>
<output>882</output>

<gadget id="calculator">882 * 2</gadget>
<output>1_764</output>

<result>1_764</result>