title: concatenate the first characters of words in a string
body: <p>Given for instance the string <code>"The organization for health, safety and education"</code>, how could I obtain:</p>
  
  <pre><code>Required_Output = OHSE
  </code></pre>
  
  <p>In the output,I require the string which consists of the first letters 
  (upper case) of such words having length more than three.</p>