Use matchsticks to make a square, 4 matchsticks to make 1 square, 7 matchsticks to make 2 squares, 10 matchsticks to make 3 squares, how many matchsticks to make N squares.
用火柴棍拼正方形，拼1个正方形用4根火柴棍，拼2个正方形用7根，拼3个正方形用10根，拼N个正方形用多少根．
<gadget id="calculator">3 * 1</gadget>
<output>3</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<result>4</result>