title: Find uppercase letters with one lowercase letter between them
body: <p>What regular expression do I need to find 3 uppercase letters with 1 lowercase letter between them?</p>
  
  <p>For example, I have: <code>sDdDSADadasAHHdHSAsdsagfGoHHHfHHHH</code></p>
  
  <p>But I need: <code>AHHdHSA</code></p>
  
  <p>I'm new to regular expressions but something like <code>[A-Z]{3}[a-z]{1}[A-Z]{3}</code> will find also <code>HHHfHHH</code>, but I only need 3 uppercase and the next one need to be lowercase. I need to get <code>AHHdHSA</code>.</p>