title: Regex to find week date
body: <p>We're receiving a file from a customer which we need to read and save some values into our ERP-System.</p>
  
  <p>the customer sends us a date in a week format like: <code>201814</code> this would mean the 14th week of the year 2018</p>
  
  <p>the customer sends this date never in the same place in the file, so the only way i think I can get this date, is by searching the string in the file by regex.</p>
  
  <p>My Regex should probably consist of the following conditions:</p>
  
  <ul>
  <li>the length of the string is always 6 characters</li>
  <li>all characters are nummeric values</li>
  <li>the string always starts with <code>20</code> </li>
  <li>the last two values have to be between <code>01</code> and <code>53</code></li>
  </ul>
  
  <p>what would the perfect regex for this be? there are many other "nummeric-only" values in the file, that's why i need to be so specific</p>
  
  <p>I know I can do the length condition like this <code>{1,6}</code> and I know that <code>[0-9]</code> matches all digits from zero to nine, but I can't see how I can restrict 01 to 53.</p>
  
  <p>Can someone help me with my regex? thanks a lot!</p>