title: Why does substracting characters gives wrong answer
body: <p>If they concatenate</p>
  <p>shouldn't be like:</p>
  <p>a = &quot;3&quot;+&quot;8&quot;= &quot;38&quot;</p>
  <p>b= &quot;38&quot;-&quot;8&quot;=&quot;3&quot;</p>
  <p>a=&quot;38&quot;-&quot;3&quot;=&quot;8&quot;</p>
  <p>?</p>
  <p>I also didn't understand why that solution doesn't work </p>
  <p>where did the &quot;0&quot; come from ?</p>