title: indexof returns -1
body: <p>When my string is <code>mail&amp;mail@mail.com</code>, the code returns -1.</p>
  
  <p>How can I solve that?</p>
  
  <pre><code>email = mail&amp;mail@mail.com
  int arroba = email.IndexOf("@");
  </code></pre>
  
  <p>I also tried this:</p>
  
  <pre><code>int arroba = email.IndexOf("@", email.IndexOf("&amp;"));
  </code></pre>
  
  <p>Any help serves me thanks</p>