title: "Missing number, treated as zero." in LaTex
body: <p>I want to get the Roman number of 2. So I use <code>$\Roman{2}$</code> inside text. But then I got an error</p>
  
  <blockquote class="spoiler">
    <p> Missing number, treated as zero.</p>
  </blockquote>
  
  <p>How can I fix it?</p>
  
  <p>Thanks and regards! </p>