title: regex 4-6 digits ending with 00, but lowest value is 5000
body: <p>i'm trying to make a regex for this condition:</p>
  
  <ul>
  <li>6 numbers max</li>
  <li>finish always with <code>00</code></li>
  <li>lowest input <code>5000</code></li>
  </ul>
  
  <p>These should match:</p>
  
  <pre><code>5000
  11100
  699900
  999900
  </code></pre>
  
  <p>These should not match:</p>
  
  <pre><code>900
  4900
  12345
  999999
  1230000
  </code></pre>
  
  <p>I browsed through the site, but without success.<br>
  I'm not very good at regex - could somebody please help? </p>