title: Extract only right most n letters from a string
body: <p>How can I extract a <code>substring</code> which is composed of the rightmost six letters from another <code>string</code>?</p>
  
  <p>Ex: my string is <code>"PER 343573"</code>. Now I want to extract only <code>"343573"</code>.</p>
  
  <p>How can I do this?</p>