There are 20 questions in a math test. It is stipulated that: 2 points for a correct answer, 1 point deducted for a wrong answer, and no points for unanswered questions. After the exam, Xiao Ming scored 23 points in total. He wanted to know how many questions he had done wrong, but he only remembered that the number of unanswered questions was an even number. Please help Xiao Ming calculate how many questions he got wrong.
一次数学考试共有20道题，规定：答对一题得2分，答错一题倒扣1分，未答的题不计分．考试结束后，小明共得23分，他想知道自己做错了几道题，但只记得未答的题的数目是个偶数．请你帮助小明计算一下，他答错了多少道题．
<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<gadget id="calculator">26 - 23</gadget>
<output>3</output>

<result>3</result>