Please add an appropriate parenthesis in the formula: 1+2*3+4*5+6, so that the result of the formula is the smallest. What is it?
请你在算式：1+2*3+4*5+6中添上适当的一个小括号，使算式的得数最小，是多少．
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">1 + 6 + 20 + 6</gadget>
<output>33</output>

<result>33</result>